I found the stalker design neat,the fallout one seems to fit in the case of the heavy power armor, scrap power armor should be usable by all mutations that don’t turn you into some big THICCO BOIIIIIIII !!!
most power armor should have the option to add a sheath/scarbab,holster and rifle sling/magnets.
I think it is farely balanced as long as the items are uncraftable example:
Neodymium electromagnets for your RM-51 assault rifle be fixed in your chest and can only be removed by the magnets having negative charge aplied (only the power armor user can remove it ) the same applies to the holster an scarbab/sheath as an explanation,or make XL stuff usable 
If power armor is huge to the point of even strapped gear being blocked the a squid girl or a plank boi can enter it thanks to their malleable limbs