Help AFTER printing? Tools, kitbashing

Ive been printing my own supportless figures for a bit and been enjoying the process. Lately ive been moving into some more complicated stuff. Its been requiring me to use some supports and cut some models in the slicer, rotate them to hide layer lines, stuff like that. Its been going great, but now ive run up against a bit of a wall. What tools and stuff do I need to clean up my minis after printing? I can glue the pieces ive cut apart in the slicer all right but the gap still shows between them, is there anything I can use to fill this up nicely? What can I use to get the little marks off left by the supports? What can I use to clean the underside of overhangs? (for example cutting a block in the slicer, you put a dowel between them. Printing that part vertically now leaves an overhang which can sag a little. The dowel no longer fits together).

I have 0 experience with tabletop gaming and assembling minis and stuff in the past. I am very new to this. Got no friends that can help me. The 3d printing side is going fantastic but I have zero idea what to do with this stuff. Some people have said hobby knives. I dont know what they are but I think theres a brand called Tamiya which makes them when I searched that. Kinda expensive would prefer to avoid it if I could unless theres no better option. Search also brought up exacto knife but that looks like something at a drs office with if im being real.

I did try to search around for some help, i saw ObscuraNox (who posts the settings at top of the sub) said you shouldnt need to do much work after printing. That is true for supportless figures but when you put some supports and have more complicated models like for resin. It leaves marks on the mini unless you have saggy overhangs etc. So maybe it is just a skill diff. Here is their post

https://www.reddit.com/r/FDMminiatures/comments/1pqnuwn/comment/nuvrtmx/

If this is not the right place please tell me where to go. Else i really need some help because i got a bunch of really nice looking prints just need some work. Ready to start learning to paint but obviously theyre not ready rn.