Retrofitting buffered fx loop into Laney HCM30

[Kostu96]

Hello,
first post ;p
I want to add buffered series fx loop and master volume control to my Laney HCM30.
I'm somewhat green in electronics, and I come up with this so far:

Would it work? Is it missing something? filters, coupling caps?
And I want to add switchable attenuation from line level to instrument level, how would I do that?
I tried to look for resources and examples, but everything is for valve amps and I just can't read those schematics
Amp has +15/-15V supply for the rest of the tl072s.