I just got the M-LOK for my gun and I have a quad rail thats left over. As mentioned you will need a barrel nut tool to remove yours and you will need a barrel clamp. Both of these items can be bought or made.

PM me and we can probably work something out on a hand guard. I also have a line on other factory parts but S&W doesn't sell hand guards etc. They keep all their parts in house for repairs and who knows what else.

As for upgrades there is a different place for almost everyone of them. Figure out what you want and then make a thread on that part for others input. After that make your own opinion and go out and get it at the cheapest or most reliable retailer.