Starting from a M4 is a good idea. The price they offered is not so good. WE is not really know for being good, more for being cheap instead.
Don't change the hop-up chamber unless you have to. Metal does not always mean better. If your aftermarket parts have difference dimension/tolerance issue, that will be a pain in the ass. Change the hop-up rubber if you feel the need.
Most people just start on a stock gun and replace parts as they broken. Sometimes you need to replace the spring (if the local field need a lower FPS), the hop-up rubber (if the stock one is low quality) first but that depends.
For your battery, make sure you distinguish the NiMH and LiPo. As LiPo have lower internal resistance, a 7.4V LiPo roughly have the performance of a 8.4V (or more?) NiMH. When it comes to 11.1V LiPo, yes, it will wear your trigger contacts faster, unless you install a MOSFET. But other than that, 11.1V don't cause any additional damage alone. 11.1V LiPo "damages" your gun because you shoots more with 11.1V.
11.1V is also not "better" than a 7.4V. 11.1V makes higher round per seconds and faster trigger response, if you are looking for those, then a 11.1V is better to you. But if you are fine with the performance of 7.4V, then 7.4V is fine for you. This is about having fun, not a match of upgrading your gun to the top on every aspects. I run 7.4V on my rifles while 11.1V on my LMG.
If you get LiPo, make sure you buy a balance charger, and if you can afford it, buy a computerized charger like the iMax B6. They are great and you will like it. Also don't buy LiPo and chargers from airsoft store, buy them from RC hobby store, offline (your local area) or online like Hobbyking.
Last edited by ccyg8774; June 16th, 2015 at 22:33..