1) Is RM500 budget realistic for 1TB? Or need add more? - more than enough for 1TB

2) What are good options for 500GB and 1TB? Kingston NV2. can get around RM350 at shoppee

2b) I have slots for 2.5" SATA and M.2. From my laptop specs I can only use one or the other. Is there a difference if I use which in terms of price and performance? - NVME M.2 is usually faster than 2.5' Sata

3) Safe to self-install or better let a pro handle it? - if you're not confident to do it, pay some one to use it. but usually can search for guide video in youtube.