I wouldn't do a big one like that either.. the more you take out in an established tank with plants, the more out of balance it can become. If your tank is heavily planted then I wouldn't do more then 50% max.. the live plants will help keep the tank clean while you are away.
I would suggest only 1 snail while you are gone- as many of them have huge bio loads, and you don't want them to make too big of a mess while you are away.
How long will you be gone?
I understand about having rules lol.. my boyfriend tries to give me as much leeway as possible, but he knows me enough to where he has to put his foot down now and again whenever we go to the stores lol
Some algae won't harm the tank, and can actually be good for it. I would say as long as you don't go past 12 hours a day, you should be fine.. just have your snail or shrimp help keep the algae maintained.