First, you’ll need the basic upgrades, common to most of the loadouts. This is the suggested order:

Barrage level 1 (100 certs) OR Fire Suppression level 1 (30 certs).

Barrage improves firepower situationally, but fire suppression is more forgiving.

Trial top gun of your choice.

This will allow you to use

Racer 1 (100 certs)

Stealth 1 (30 certs)

Gatekeeper (550 certs)

P2-120 AP (875 certs)

Reload upgrade 1 for AP/top gun (150 certs each)

Gun magazine sizes 1-4 for AP/top gun (1/10/30/50 certs per level)

Gun optics of choice for AP/top gun (1-500 certs each)

From here invest evenly in upgrades as certs become available.