I cannot comment on upgrading it because my SPR mk2 is bone stock. What I can tell you is that it has incredible range/accuracy right out of the box with an 11.1 lipo.
My suggestion would be to just run it as is while you learn more about upgrading.
I remember getting my first airsoft, a G&G M14UBR for about $530. I looked up a few things on mods/etc and thought "I could do this".
I ended up taking apart the gun, losing all kinds of small parts and the more I attempted to fix it, the worse it got (started with a broken motor cage which I attempted to JB weld, then it did not fit in the gun. I got out the dremel to make it fit, then upon piecing together the upper and lower, I ended up pinching the wires enough that they had to be saudered, dremeled the inside of the lower so everything could fit.
Looking back, I can only wish I was not so stupid thinking I knew what I was doing. It would not have been so bad if it was a beginner gun, but when its an expensive G&G proline, it's heartbreaking to have it as a mere display piece.
At the end of the day it's up to you, but I have been into airsoft for about 4 years now and feel no need to replace anything in my SPR 2. (If it ain't broke, don't fix it) I have had it since June and it has been nothing but just as great as the day I got it.
If you really wanted to look into mods for this, check out the Umbrella armories website and you can see what they use to modify their $1100 (USD) Krytac SPR DMR.
My suggestion for a first upgrade would probably be a a Prometheus Laylax stainless steel barrel (there is one specifically designed for the Krytac) which I believe is 410mm 6.03. This is a fairly easy mod (no need to open the gearbox) and if you can also learn to R-Hop (certain retailers like blackblitz can R-hop a barrel you order from them for a few extra $$.) this would likely get you a great performance increase but will cost roughly $80 for the barrel and about $50 for the R-hop installation (if you choose to have it done professionally.)
Whatever you decide on, proceed with caution and best of luck