If you're just starting this project here is my advise.
Magnets!!!!
With one to two sets of magnets per Spc. Weap. trooper you can have all the options. Or at least room to expand when the new dex drops soon. Same for the Valk. A valk is good, but if you magnetize the weapon mounts you could have a Valk/Detta combo that you can have either way. It's more initial investment, but it pays off big in the long run, trust me. I've done two Dettas with magnetic cannons and love them.