Thanks for the great questions.
Reputation does not directly factor into becoming a witness. Someone with a higher reputation probably has a greater chance of being voted on, but that is it.
As I just found out from @gtg earlier today, delegations do not affect the amount of voting power each person has, only vested shares (not deletaged shares)
So, the use of bots are not a direct factor in becoming a witness, but there is of course an incentive if your run bots to be a witneess so you can insure the bot revenue remains.