Dont waste your time upgrading everything.
Max level only these things: Sentry(only one. The rest will work eventually as chockepoints)
Codegates (avoid access from 2 nodes) scanner(connected with your codegates)
Beams,icewalls both from level 10 they are very quick strong and cheep to compile. Just remember. To be able to maximize sentry and the rest you will need core level 12.
Anything related to Hackers that doesn't fit in another forum