(1) Try and get the filter up and running before you leave -- dirty water isn't good.
(2) Not sure about these auto-feeders -- like NippyF, I've heard bad things
(3) You have guppies along with you betta? what size tank? (be careful -- if they are fancy guppies, with large colorful tails, your betta may attack them). Also if you have too many fish for your tank, that could be bad.
(4) If you have someone come in to feed them, make sure they know how much to feed -- most beginners will over-feed. Maybe leave out pre-measured portions?