Hi bro. Same like u, i just jumped from FW to marine. First of all, welcome to the club!
1) You can buy live rocks almost everywhere. Pasir ris farmway, Jalan Bahar, etc. Theres so many shops selling live rocks and sands. Some bro here also do sell of their live rock! (i do have a large rock if u want hehe)
2) Im still new, so im just sharing my media. Im only running biohomme plus which i brought over from my FW back then.
3) Some fish farms do sell NSW. etc Iwatna, Ah beng, Jireh so on..
For the advise on the "cheapest" set up, i used to be like u. Always wanted to have the cheapest set up. But end up i splurge alot AT THE BEGINNING, and now im reaping the rewards. You can try readong up the thread i started on "Cheapest set up" to get a rough idea how our other bros run their cheap set up successfuly. Hope my advice help u. Cheers!