rules about votes will slightly change in next hardfork (HF19 - https://steemit.com/steem/@steemitblog/2hfxx1-pre-release-hf19-linear-rewards - really great news :)), but right now you can vote for 40 things with 100% voting power.

Your current voting power can be checked at: https://steemdb.com/@ivanli (on the right)

You can vote for 40 things with 100% vote, or for 80 things with 50%... or any combination. You basically have like 4000% voting power to spent daily (this will change in next HF - default vote will be stronger).

If you vote for 400 things a day, your vote will automatically dilute on that day.

Voting for comments is not good or bad. Value of each post/comment is subjective for every voter, so only voter can decide whether he or she want to vote for that :)