When you install a roller cam in a non roller block you need some way to controll the latteral position of the cam, thus you use a cam button. The roller block is machined for a thrust plate, this fits between the cam and the drive gear allowing minimal movement.
Yes you use a different cam if the block wasn't set up for roller, the front of the cam is different where the gear attaches. Use the correct cam for the correct block, use a bronze gear on steel billet cams, valve springs for roller cams generally have lots much more seat pressure than non roller, yes you have to check for interferance allow .050" clearance, several types of lifters are available, go with cam grinders recom, do not mix hydraulic with solid grinds, push rods will have to be sorted out to the combination you are running, older style rev kits tend to not fit the newer aftermkt heads well,not enuff surface area on the bottom side of the head. aftermkt heads usually have enuff spring and guide clearance and travel, but you have to check.