If you want SMGs then yeah, I thought he wanted a rifle.
Would not recommend the CGS, absolutely awful system, poor quality control, avoid.
That HK416 is a steal but having chatted to the owner it needs a lil TLC. (Still a great deal).
Don't get the KWA MP9 as your first, it's a gun I've watched experienced techs curse to high hell. It can run great, but only after replacing every part inside it and fettling it just right.
The Tec-9 is cute and there's a handy Explosive Enterprises video deep diving on it. It's very meh, can't really fix any of its issues, has no aftermarket. Nice if you want that Miami Vice look but basically any other GBB SMG will outperform it.
My pick would be the 416 with the understanding you might have hop issues, second is the MP7 noting that it can break its backplate.