There are many ways to go about this. First of all, I would highly recommend getting some good brewing software. BeerSmith is the one I use, and I like it. It's not just for all-grain, it can be used for extract batches as well. In the software, you can look at sample recipes and select style guides to let you know what SRM/IBU/OG/FG/etc the beer should be at. So you could start building a recipe from there, or modify an existing one. One other thing you could do (saw you have a kegged pumpkin ale) is trying a normal recipe but adding stuff to it. You can make some very unique beers just by adding a different ingredient to it. Also, you could take a beer that you like and figure out how it could be improved. Don't think about it; just take the first thought that pops into your head like "bitter" or "too light" or "not smooth" and move on from there.
As far as bulk ingredients go, that's more of a preference thing. It will save you money...but if you buy bulk ingredients and then find out you don't like a certain grain or hop variety, well you're stuck with it. I wouldn't start buying bulk until you find your "house recipe" that you know you'll be brewing forever. If you have limited space, you might not want sacks or tubs of grain sitting around. If you have rodents or insects that like to explore, that is another consideration. Also, even though buying bulk does save you money, it requires a significant initial investment because although cheaper, you are still paying for bulk. I'm not saying you shouldn't, but these are some considerations.