Transaction fees (at least early on) should go down dramatically. We are adding 1024x the throughout but demand won’t go up that much. Therefore, there will likely be an abundance of block space in the early days of eth2
In PoW there’s a minimum fee of sorts where below that, it’s not worth it for a miner to include a tx due to uncle risk. In PoS this risk doesn’t exist and therefore fees could get very close to 0. At least that’s what I’m expecting.
Most validator profit will come from staking rewards. You can find expectations for that here