Hey sorry if this is repetitive from my previous messages but?

I just want to consolidate all the advice into one plan. So January 2010, I have run two sub 24 minutes 5 Ks and have set a target of running 5K in 20 minutes by December. Now do you think taking just under 5 minutes off my time in one year may be too much? How much can I take off every month from my time. Also what kind of things do you suggest I do for training and eating. I like to eat snacks and don't want to cut them out. I eat healthy meals and drink a lot of water. I run 3/4 times a week and do a couple abs work outs too but no weights. I haven't done any speed work as such as I prefer to just run the distance I choose to run on a given day but I will incorporate one speed work out a week. Thanks a lot.