Okay, let's start with this:
SPOFS X,y X=NUMBER Y=NUMBERThis is probably what needs to be done first, it'll make things easier, each level can have a different location by just inserting what X & Y equals. As for collision, don't use:
IF Y>145 THEN Y=145Use the SPHITSP command for the tiles and your player sprite.
IF SPHITSP PLAYER,BLOCK THEN...