What is the best way to build on toxics for def and production?

3 +10's
3 obv

or what other way do you guys build on them for maximizing the production on them?

This is not how any of mine are built, but i'd imagine a good build example would be;

16x MR Very Large Toxic Build - 57 Space

2 +12 Buildings - 36 Space - 24 Mining
2 Tri-Phase Cutters - 2 Space - 6 Mining / 600 Attack
2 Adaptive Spires - 2 Space - 4 Mining
Stripcore Mine - 1 Space - 4 Mining
XTS-10 Injector - 1 Space - 3 Mining / -150 Population
Hypergate - 1 Space - 2 Mining

3 Quasi Chaos Minefield - 6 Space - 3600 Attack
2 Lazuli Pylon - 2 Space - 1200 Invasion Defense
2 Domain Walkers - 2 Space - 1200 Attack/1200 Defense
1 Archaic Stasis Cell - 1 Space - 500 Invasion Defense(+200 Pop)
1 Astrobiology Ward - 1 Space - 500 Population(+50% Pop)
2 Lazuli Dark Mine - 2 Space - 1200 Attack(+25% Attack/+25% Attack) < The 25%'s apply one at a time, not as a combined 50%.

That gives you 516 Mining - 1095 Population / 1200 Defense / 10312 Atk / 1700 Invasion Defense < Before Legion Bonuses & not including the possibility that a person might irradiate this planet or add passive defense.

Sulcation portals are nice too, they add 2 mining and 200 pop for 2 space. Very handy. An Assimilation Locus is also a nice touch if doable.

I stuck 3 top tier claoking structures on a toxic I turned into an iradiated planet. I get about 475 mining out of it.

I would say that might be good for Irradiated planets but 16x vl toxics get very common when you primarily hunt NPCs. I just do 2x12 mining, phase cutters and mix of def/atk and call it a day.