How do i avoid detonation.
Its the big killer isnt it?

I was thinking of installing a mixture gauge but is it worth it? Is it easy?
Also i have a Apexi power fc, if i get the handheld thing will this give me any decent information on the engines mixture and other longevity info.

 

Plan and install your mods carefully after researching them thoroughly - or don't mod at all.

 

Good advice, my car was bought pre modded, fmic, filter, exhaust, bov, apexi,
Is the key to just keep it running quite rich through the rpms

 

No, that's just the band-aid way to do it. You won't be able to read a/f mixtures and make any proper adjustments with the PFC unless you get a wideband O2 sensor (and datalogit software or something similar). Do some research, all the info you need is in the forum archives.