I really liked the Avent Isis pump. I could pump 1-2 four ounce baggies in 1/2 hour (depending on time of day, etc). I was going to school, so I pumped every morning and froze the milk (we used the liner bags for easier freezing). If you're only pumping occaisionally I wouldn't get an electric pump, it just isn't going to be worth it.
As far as taking a bottle, it may be the rubber nipple just isn't you, more than that the milk isn't the same. You can start teaching him to drink from a cup soon (I started with my babies about 6 months old). Not a sippy, he can learn a regular cup. Start with a tiny bit of breast milk or water in a small cup. I always started by holding a cup close to his mouth and using a baby spoon to put some in his mouth (I had already introduced rice cereal). I got the cup closer, and made sure he saw that the milk was coming from the cup. Pretty soon, I would put the cup to his mouth and tip it up to give him just a little bit. It's going to be quite messy at first, but most babies catch on quickly.
He also will be starting solids soon if he hasn't already. You can leave the baby food and some milk with a cup when you leave him with your mom, and he should be fine.
As far as the wedding, though, I would pump breastmilk (as much as you can) and supplement it with formula if it isn't enough. If he's already eating some solids by then, have those for him too. Just remember to wear good nursing pads (or double up), you don't want to have any embarrassing leaks!