not an expert but I'll try to answer :
1) I leave mine without the backpack lock, since the era of the infamous breakage of the 1/48's BP8 part.
2) maybe you can try wiggle it a bit. what I always do on mine is hold both legs in battroid mode, with the backpack facing you, with all four fingers excluding your thumbs. Swing the wings away so you can access the nosecone's bottom with your thumbs and press the forward section of the nosecone away gently until the metal part pops out from the slot. wiggle a little and slide the nosecone back down (since you have to slide it up when transfroming from Fighter-to-Battroid)
3) normal
4) not an expert on this so Ill let others chime in.