It's not time to modify yet. First determine what your use for the gun will be. Then GO SHOOT THE GUN. Spend some time at the range and get to know what you like and dislike about the gun as it is. If you decide you want a particular mod, see if a LGS has a gun equipped with that mod that you can get your paws on. A rifle is all about feel/ergonomics. Try not to "drink the koolade" on every new tacticool specops gee wiz gizmo and gadget that that the internet throws at you. Just because Chris Costa has it doesnt mean you NEED it. Magpul AFG is a prime example. 2 years ago they were all the rage. They were as common at the range as baggy pants are at a rap concert. People are starting to get away from them now and or modifying them to something better suited to their needs.
So go slow and don't envy what other guys have on their guns. Their guns suit their needs. Your needs will be different. Only you can determine what your needs are. If you are honest with yourself you can build your ideal gun faster and waste less money. I have a box of "stuff" that I put on and then took off my gun. All of it is wasted money. All because I "WANTED" something I didn't need.
HAVE FUN !
When injustice becomes law, rebellion becomes duty.