Definitely stick to the core rules and don't assume everything in Pathfinder works as they did in 3.5.
We made a point of looking up even mundane rules when we switched. That identifies the changes pretty fast. Many of the feats commonly used in 3.5 have changed, so ensure you give those a read before anyone commits to taking, much less starts using, them.
I would also definitely stick to 15 or 20 point buy, 30 is way to high.
We've been using 20, which is pretty much equivalent to 28 point buy in 3.5, which highlights another change in that Pathfinder starts characteristics at 10, not 8. So a character with, say, 4 14's and 2 10's who costs 28 points in 3.5 costs 20 in Pathfinder. As a result, especially on the switchover, it's easy to miss the fact that less points can buy the same stats.
Note that the pricing also changes, with the price going up at even, rather than odd, numbers (ie the characteristic point that bumps up your bonus).
For 30 points, you could have 14's across the board, or two 18's, 2 12's and 2 13's. Hey, take 3 18's and 3 10's (if you dump one of those to 7 the other 2 can be 12's).