1.If you're going to be focusing mostly on sprint distance, you NEED to do speed work. I do a lot of sprints, and at this point in the season I'm doing lots of zone 4 and 5 work. You DO need to figure out what a "good physique" means to you. If you want to look like a bodybuilder, you won't be able to be as fast in tris, but you might pick up more girls. If that's the case, go ahead and do the heavy-lifting. IMO, you can be fairly on the jacked side and still be good at shorter tris. Swimming and medium-intensity weights will build your upper body to a not-embarrassing-without-a-shirt level and will let you be a faster triathlete. Either way, you're not going to look like a cyclist (unattractively bird-chested). The volume of doing 2 weight days plus all of your other training isn't a problem as long as you get your body used to it.

2.No, but you might not swim as fast, which is ok. You're training to be fast in races, not to be fast in training.

3.It's only too much leg work if you build into it too fast. Don't double your volume in just a few weeks or you'll get injured. The safest way to increase training is to either increase your volume by ~10% or your intensity by a little each week...one or the other. Ex: 10 mi @ 155 bpm, 10 mi @ 160, 11 mi @ 160, 11 mi @ 165 over four weeks, doing similar stuff with the rest of your training. It's not always that cut-and-dry while you're going from base to tempo to interval work, but you get the idea.