Echo 1 STAG-15 A4
6.03MM Tightbore
m120 Spring
Polycarb piston and piston head
Systema Bushings
New Air seal nozzle
Steel spring guide
Would that work out well? Any other things i should get upgrade wise?
What barrel? For 6.03mm, Madbulls are great. If you can spend a bit more, Prometheus are nicer. You might not see much of a performance difference between the two, the Prometheus will just have a longer lifespan since it's SS. You can still put plenty of rounds through a Madbull though. (it's not like it needs to be replaced every 40,000 rounds)
I know the JG Enhanced models come with metal bushings, not sure about the E1s. I would think they do. You might check which size bushings the E1s come with if they are nylon.
Keep the stock piston and piston head. If the stock piston is the creme colored one, then it is very durable. Just make sure the AOE is adjusted. Piston head is good too, you may just need to replace the O ring with a #14.
A bearing spring guide is a good idea. It should have a metal spring guide stock, but replacing it with a bearing one is a good idea. Or keep the stock spring guide and add a bearing piston head. (Element POM/Red piston heads are great)
New nozzle is always a good idea. Stock clone nozzles typically are leaky.
Reshim and regrease the gears too while you are at it.