Newbie in Hardcore single player asking for help answering questions I have

Don't really understand why my last post was removed it didn't violate any of the rules posted on here. I have gotten great help here in the last week or so

I started off in hardcore offline and i am currently level 27 and in act 3 normal and need some help.

Here is my specific questions that I haven't found concrete answers from on other reddit posts or Google.

I have 18 points into raise skeletons. I have corpse explosion. I have amplify damage I use but people told me to put points into decripify but not sure what I use that for given specific situations? I mean I understand the mechanics of it but don't understand when I will use it over amplify damage.

I know i have to put 1 point into revivive. Do I not max revive? I remember when I played like 20 years ago people maxed it out but people don't do this anymore? Some guides say to max it and others say put 1 point so im not sure why I would only put. Point into it for 1 summon? I feel stupid not understanding it?

Also I need to put 1 point in summons resist still.

After maxing out raise skeleton I was told to max out skeletal mastery.

Also do I only use clay golem? The guides I read say use clay golem however llamas hardcore necromancer playthru said he would use iron golem sometimes.

I am using Emilio act 2 prayer merc for now. Do I change this at some point in nightmare to might? Or go another route due to hardcore?

Does decrepify work on spell casting targets like the fire breathing guys or lightning guys? I can't find a definitive answer on Google and don't trust Ai answer im getting.

I have Nadir and stealth runewords. I don't really understand why I was told to use nadir though as there are only 9 charges for cloak of shadows and it costs a ton to recharge. Would i use it only for boss fights or something?

Can anyone tell me other runewords to look out for as I level?

Should I just get a shield with 3 sockets as soon as I find it and fill it with highest diamonds I find so I can better resists as much as I can to help survival? Or do I go for a head as my offhand for +skills? I see the head mentioned in regular characters but I see people mention shields in hardcore but ay same time I was told to get a head when I started this journey so im not sure what the answer is. I'm not a good player being a newb, so I figure protecting myself is best way?

Again I started brand new and have no gear so im trying my best to hunt for better gear as I level. I have about 50% magic find from rings, boots, gloves. Should I wear that magic find now or wear regular gear with resists on it? Part of me wants to be safe but other part of me wants to get items since this is my only real chance and I need to start somewhere.

Thanks for the help! Have a great day!