What internet data usage can I expect when mining in pools?
No, it's much less than you think. If you look at the Stratum protocol, you'll see that the pool server doesn't send you the full list of transactions of a block, but just their hash (in a merkle-tree fashion). So, each new block that they'll send you is only a few hundred bytes, every ten minutes or so.

Your miner will likely report shares, but this should be infrequent (once every few seconds at worst), and this is a few dozens of bytes.

All-in-all, you should be looking at less than 100kbyte / hour.

PS : you can join the lottery or... you can mine for science at the 3SUM pool (disclosure: I'm its author).