as many have stated starting with a baseline model and adding features that you want is normally the cheapest way to go and offers the best chance of being happy with the end result without resorting to buying a second AR down the road but if the MP15T already has a decent amount of the features you are looking for then I say go for it.
ignore my complete lack of capitalization. I still have no problem correcting your grammar.
I never said half the crap people said I did-Albert Einstein
You can't believe everything you read on the internet-Benjamin Franklin
Bean counters told me I couldn't fire a man for being in a wheelchair, did it anyway. Ramps are expensive.-Cave Johnson.