Based on what you've stated, you have a lot of good options. I'd recommend that to get started, you find something like a DPMS that's already together. Shoot it and get it broke in, and then see what direction you'd like to go with a barrel, trigger, and possibly free floating handguard and gas block options. You will undoubtedly be able to do enough customization on your own at that point to feel comfortable with a build, should customizing an off the shelf rifle fail to make you happy. You don't have to pick a DPMS to start with, there are plenty of good brands to choose from too, it's just a suggestion.