I found a Terra that has 2x mega rich artifacts, very rich mining, and abundant research, should I make all structures artifact or should I balance it between mining and artifact?

Artifacts is what I would focus on.

I mean should I put it all in artifact or put some in mining most in artifact.

Well, it has a higher artifact, so I would say put mostly all artifact. Avoid wasting space for mining. Although the mining stat is quite good, it should be avoided unless you are seriously suffering from credits shortage, then only should you put some mining structures.
Note that this planet is sufficiently good enough for mining chassis, but comparatively not good enough for the normal mining structures (when compared to the artifact production)

I have 5000000 at rank 50

hate to say it but that's not much 5 mil.... the size 16 +8 production buildings cost 50 mil + 20 Krenite.. so a little over 80 mil EACH building... and the size 17 +10 production buildings total about 275 mil EACH building... i'll just say i make A HELL OF ALOT more then 5 mil per hour and i'm always out of cash due to those reasons... and honestly... you should keep planets specialized in what they are the best for in production.. you get the most bang for your buck, they are easier to go around and upgrade and find... and why would you want to waste a +250% production on artifact just to get a +150 on mining? or whatever... use sense... you get the most going with the best on planet.. not splitting it around

I dont get 5 mil per hour, I get 200k an hour, my total is five mil. Also, I am nowhere NEAR that high in the research trees, I balance, so Im up to 5th tier in every tree.