The Terran Republic was the primary facilitator of the Federated Commonwealth alliance aligned against the Concord of Kapetyn. You can imagine the 4th Succession War I assume.
The sixth employer of the Wolf Dragoons was the Terran Republic who gave them the planet of Outreach as a holdfast for their service. Again see the similarities but there are subtle differences.
Again I'd like to not comment on the "Clan Invasion" maybe we will one day but not now.
I never loved sub capital weapons, I was just going to have other capital weapons which could fit on dropships adapted to do so. No reason not to. Yes new innovations would also occur as indicate. Not super Star League high tech but common sense Level 1 upgrades.
In regards to cost modifiers I figure they decline after a while say end of the 1st Succession War. As they proliferate the cost and technical knowledge spreads out.
Star League (Level 2) tech is as in canon LosTech. Examples remain here and there but they are rare and hard to impossible to fix until the Helm Memory Core that is....