Congrats on your upcoming trip! I think 4 nights is perfect.
As for which resort...I am partial to GC. I am a big fan of WL at WDW, so GC really reminds me a lot of WL. However, DLH is nice too. I haven't stayed there in a long time, but if the pool is important to you, DLH's is the best in terms of theming. Also, I'm not sure how much you know about DL, but keep in mind (esp. if budget is a factor) that you can walk from many non-Disney hotels to the parks, so it's not necessarily a "must" to stay onsite.
As for the meal plan, I've never done it myself, but the reason is that I don't really think it's worth it. Unlike WDW's plans where you can save money by ordering more expensive items, DL's plan is kind of a voucher system -- so you might get one breakfast voucher per day, a $10 voucher, a $5 voucher etc. (there's another post around here somewhere with the specifics), so in some ways, you can actually lose out if you don't use the full amount. I think the primary reason people might use them is to be able to budget and pay things in advance.
I assume you're travelling with at least one other person? You should be fine walking in the immediate vicinity of DL, like across Harbor Blvd (still use caution and keep your eyes peeled though). The most we've ever encountered there was an occasional homeless person asking for money or food.
However, there really are lots of food options in the hotels and Downtown Disney, and prices pretty reasonable.
As for the attractions, I agree with iceskatejen...go to the ones that have WDW counterparts, there is a definite difference! With 3 full days, you should be able to hit just about everything.
Oh, and one more thing regarding Fantasmic! If it interests you and it fits within your budget, you might want to consider the dessert buffet. There is a thread about it with the details. It's pricey, but you're guaranteed a seat, and you get dessert and drinks. Like iceskatejen said, if you don't find yourself a spot hours ahead of time, you will probably be standing somewhere craning your neck to see the show.
Happy planning!