Cheat Sheets for Rules? Starting Questions

Howdy, I'm going to try my hand at DMing for my two room mates who've never played, I'm completely unfamiliar with 5e, I've seen cards for spells and such which seem like they'd be helpful for three noobs. So far I've ordered the Player's Handbook, the DM Guide, and Monster Manual (we'll all use the one Players Handbook to cut costs), Im also going to order a dry erase battle mat, and a set of dice for each of us. However I'm afraid my players will suffer from analysis paralysis and was hoping maybe there is a premade cheat sheet for the rules and what kinds of actions they can take on their turn. Also I was wondering if their is any app or solution to figuring out how many monsters to throw at them without it being too easy or too challenging, like an app you put in what PCs there are and what will be an appropriate challenge. I'm afraid I'll lob too many soft balls at them and they'll get bored, or I'll over estimate them and they'll die.