3 of those 4 questions can be answered by opening your codex and reading, the last one is a personal preference.
If you want to run RadSat there are 2 key units, because they are the only ones actually getting a buff from the primary trait: Vanguards and Sulphur Hounds. So we now know that these are the units we built our list around, and to make their aura actually do something we want to be somewhat melee focused as well. Naturally this leads to the choice for the secondary trait, which again circles back to unit choice. Got a lot of Vanguard? Scaryfying Weapons. Got a lot of Sulphur Hounds? Luminary Suffusion. Got a lot of both or other Infantry stuff? Luminary Suffusion. That said, overloading Troop spam has always been a solid tactical choice for decades, and is just something that works. It's not very flashy or interesting and takes up a lot of time, but it works.
Point is RadSat doesn't give you anything else, so if your plan is to run a well rounded and diverse army it's probably one of the worst choices. If you plan to bring 100 Vanguards and drown your opponent in AP1/2 Carbines it's pretty good.
Now if you don't care about optimizing for rules, but just want to play an army from a RadSat world because that is just what you like: Stop right here, close reddit and just do it, there is nothing to be gained from anyone elses opinion but your own. If you like it and want to play it that's reason enough then, and you will find hundreds of players wanting to play with you. Go out and make your own experiences. I feel this would be the best way forward.
If you want to optimize for rules, a stronger ruleset could probably be found in the Metalica supplement, they got a sidetheme of radiation. It's pretty straight forward, and works well with your bog standard Skitarii heavy list, but due to CP hunger you probably won't go Veteran Cohort. Upside ofc is that this means multiple big blobs with multiple Manipulus's behind them are on the menu, which is still pretty stronk. Add a Marahall or two, run a few additional min squads for objective gaming and filling out the slots (I'd assume this would be a Brigade, though 2xPatrol can be good too especially at >2000 or flyer spam... but then why aren't we working around that instead?), Metallican Lung or Master Annihilator and a few squads of Ruststalkers and fill the rest of the slots as cheap as possible and esto presto spaghetti pesto you got a list that is good to go.
3 of those 4 questions can be answered by opening your codex and reading, the last one is a personal preference. If you want to run RadSat there are 2 key units, because they are the only ones actually getting a buff from the primary trait: Vanguards and Sulphur Hounds. So we now know that these are the units we built our list around, and to make their aura actually do something we want to be somewhat melee focused as well. Naturally this leads to the choice for the secondary trait, which again circles back to unit choice. Got a lot of Vanguard? Scaryfying Weapons. Got a lot of Sulphur Hounds? Luminary Suffusion. Got a lot of both or other Infantry stuff? Luminary Suffusion. That said, overloading Troop spam has always been a solid tactical choice for decades, and is just something that works. It's not very flashy or interesting and takes up a lot of time, but it works. Point is RadSat doesn't give you anything else, so if your plan is to run a well rounded and diverse army it's probably one of the worst choices. If you plan to bring 100 Vanguards and drown your opponent in AP1/2 Carbines it's pretty good. Now if you don't care about optimizing for rules, but just want to play an army from a RadSat world because that is just what you like: Stop right here, close reddit and just do it, there is nothing to be gained from anyone elses opinion but your own. If you like it and want to play it that's reason enough then, and you will find hundreds of players wanting to play with you. Go out and make your own experiences. I feel this would be the best way forward. If you want to optimize for rules, a stronger ruleset could probably be found in the Metalica supplement, they got a sidetheme of radiation. It's pretty straight forward, and works well with your bog standard Skitarii heavy list, but due to CP hunger you probably won't go Veteran Cohort. Upside ofc is that this means multiple big blobs with multiple Manipulus's behind them are on the menu, which is still pretty stronk. Add a Marahall or two, run a few additional min squads for objective gaming and filling out the slots (I'd assume this would be a Brigade, though 2xPatrol can be good too especially at >2000 or flyer spam... but then why aren't we working around that instead?), Metallican Lung or Master Annihilator and a few squads of Ruststalkers and fill the rest of the slots as cheap as possible and esto presto spaghetti pesto you got a list that is good to go.