For testnet, my understanding is we are limited to 64 validators.  For mainnet, I believe it will increase to 100 validators.  The list of validators is based on the ones that have the top votes.

But how does a validator get selected for the block reward? 

Is it a simple round robin approach, so for testnet, each validator has 1/64'th chance of being selected?  Or is it weighted so that the validators with the most votes always get the reward?  Suppose there are 1 million votes cast.  The top validator has 100000 votes and validator #64 has just 1 vote.  (I'm making numbers up for simplicity.)  Does validator 64 have a 1/64 chance of getting the block reward or only a 1/1000000 chance?

I understand with the launch of the mainnet, those of us who spent 1000 SEM to be a delegate will get that amount "refunded".  Will we get the keep the delegate status in mainnet, or need to spend our refunded 1000 SEM again to get it back?

Are votes only done in whole numbers?  (i.e., can there be a 0.05 vote?)

(I apologize for the basic questions.  The wikis and FAQs seem to gloss over a lot of this--and it's possible I may have missed the section covering it too.)