Questions from a fairly new DM

First of all: Which edition?

Your players are playing fairly efficiently, actually. Your wizard realizes that she can't do a whole lot with her low level spells, so she uses a bow (I'm guessing she's an elf?). Though she should be using spells to make her better at combat.

At level two, that does seem a bit high. Remember that druids can't wear heavy armor, or any metal armors, so she might not have realized that. What is her Dexterity score? A high AC she should have is somewhere around 18 or so, that's assuming she's wearing hide armor, using a large wooden shield, and has a dexerity of 16.

Your party using ranged combat is pretty smart of them to do. They don't have front-line melee combatant, I'm assuming, so really the only person who can really last in melee combat would be the cleric, if he's built to take advantage of heavy armor and melee weapons. If you want to give them more of a challenge, start keeping track of ammunition they use, or use enemies that have spells or potions of entropic shield or protection from arrows.

Part of your questions depend on what edition yo're playing, so it would be good to know that.

You have three casters, so it's not entirely odd that you're only in ranged combat. That's just kind of how it goes. After all, caster (minus the cleric) are generally pretty squishy so they don't like to get near combat. The key though isn't to punish them, but figure out ways to punish them. You mentioned drawbacks, which there definitely are. Enemies that are behind cover (for instance hiding behind trees or walls) are tougher to hit. Also most spells generally require you to have line of sight with your target, meaning walls and such can block that too. Also you take a penalty on your attack rolls if your opponent is too far away.

For the wizard, that's also partly a consequence of her being a wizard. At low levels, there generally aren't a lot of useful spells, and you don't have many of them. So she might be trying to save them until she needs them (why burn one of your only two-three level 1 spells on a rat when you don't know what you could be fighting later?). Also since she's a wizard, isn't entirely useful that she just didn't prepare anything useful. For instance she could have prepared things like Disguise Self and Unseen Servant instead of Magic Missle, and you're only throwing combat at them. So look into that a little.

For the final issue, that is pretty crazy high. (Assuming you're playing 3.5, 'cause that's what I know) The best armor a druid can wear (from the PHB, 'cause I don't know if you're using any supplements or such) is hide armor which provides a 3 armor bonus and a max dex bonus of 4, which gives you a max AC of 17. They can also use shields though, and a heavy wooden shield grants 2 armor bonus, bringing your total to 19. If your druid has a 20 dex, they could be accidentally mistakenly applying the extra +1 over the +4 dex limit of the armor, which would be your 20. However with a heavy shield, they wouldn't be able to use that hand for anything, meaning they wouldn't be able to use a bow or such (since you mentioned they primarily use ranged attacks). Another possibility if they're not using the shield, is that they're mistakenly thinking that since they're level 2, they can cast level 2 spells. So they are casting Barkskin on themselves to gain additional armor. So it is possible to have a high AC, but it's likely that your druid is doing something iffy.

1. That doesn't feel normal. Have the enemies go for cover as they approach, or bring tower shields. In d20, a Tower Shield can provide Cover meaning they can't land ranged attacks while the enemy approaches. It results in you taking away their strength while giving them a chance to react and adapt.

2. I agree with your plan. Have an enemy use the kind of wizard spells on the party that you want the wizard to use. If you're using D&D 3.5, I'm going to suggest utility spells and debuffs like Master's Touch and Forcewave. Swatting the party with Guided Shots or True Strikes from max range would be hilarious, play their own methods against them but better.

3. Yeah, that's high. Any fair encounter for their level isn't going have enough to hit, unless you're cheesing them with True Strikes. Creatures with enough base attack to hit have bad damage (Ex, Hawk; +5 to hit but 1d4-2 damage).

I feel like your party needs to fight an Ant Swarm; deals damage automatically, immune to weapon damage. Only CR1 so it's technically fair. http://www.dandwiki.com/wiki/Ant_Swarm_(3.5e_Creature)

With your wizard: put in challenges that can't be solved by arrows. Magic is a huge utility belt full of immensely useful things. Give the party things to do that can't simply be solved by combat to get them thinking laterally! They have to cross a lake of lava/cool down the massive boiler in their boat that's about to explode/get rid of the huge amount of wanted posters the noble's made to frame them with. Once they've started to think about applications, eventually they'll figure out that you can do these things during combat as well.

1. Not really normal as far as my games go but there isn't anything wrong with it. You don't have to try and box them in and certainly don't just don't pop enemies next to them just because they have a valid tactic on dealing with melee npcs. Stop just sending in wave after wave of melee monsters and mix it up. Almost every single low CR humanoid monster is capable of using ranged weapons of some sort. Also you can have your melee monsters charge into the party to close with them. Unless they pick up feats (point blank shot?) they will suffer massive penalties for firing into combat.

2. Nothing wrong with this. Spells are in short supply and people tend to want to hold onto them for clutch moments. Unless your party is going to rest constantly so she can refill her spells in between every few combats she is actually playing pretty well. In a few more levels when she has more spells and she will probably shift into casting more. For now just leave her to play the way she is.

3. Seems high. Look at the equipment section and see how much AC the armor provides and how much dex bonus she should be able to use.

Edit: Other tips

Try not to think of the game as "DM vs Players". You are judge and creator. Realize that everything you pen down for the PCs to deal with is going to be overcome by them, and that is a good thing. Do give them a good challenge though and mix things up a lot. Don't just have your monsters run up to them and attack them like it is a video game, have them take advantage of cover and use flanking. Use traps and puzzles as alternatives to combat. Don't shower them with magic items, it will seriously mess up the balance and make it that much harder on you. Drop in some role play encounters and give them small tasks at first, they don't have to start off trying to save the world.

Shield walls man. Have a formation with full length shields engage them. Make sure they absolutely have to get past the wall and it's guarding an entrance to somewhere they need to be. That should at least get them to start using some real tactics; especially the Wizard.

Ranged is smart, it's apparently a combat method that tends to petter out quickly and suck at high levels.

Try a couple mooks with the feat-chain to get Deflet Arrow once/round each. Maybe have some Skeletons wander out of somehwere (non-bludgeoning or magic damage is reduced by 5).

The Druid seems iffy, unless they are fighting defensively all the time and have 5 Ranks in Tumble for some reason, or bad feats.

I assume you can look at your players character sheets and see what they have. Try putting in a trap or two, or even some obstacles that would benefit from a good Jump/Balance/Whatever check, preferably to expedite escape from something? I do agree with the notion of periodic enemy spellcasters "showing them how it's done". Maybe offer up a re-usabls spell-storing arrow for them to fight over and feel like the magic is useful.

Also, look up "The Angry DM", and read the article about "How to Build ***king Awesome Encouters".