Hey there,

1. The max amount of delegates you can vote for is 101, but only 33 in one go.
2. You technically could vote for all pools and thus get the highest profit, but you should make sure they are trustworthy, online on Ryver (or per E-Mail), have an extreme high uptime and support the testnet
3. AFAIK There is no difference currently in your voting weight no matter if you vote for only 1 delegate or 101. However, I think it was mentioned that this could change, so that the smaller stakeholders get more "powerful" in comparision to the big stakeholders. If this is going to happen, there definitely will be announcement.
4. Your votes are casted indefinitely until you remove them from your vote list.

Hope I could help out. If you have anymore questions, feel free to ask! There aren't any stupid questions 

- Daniel