I have an older LG OLED - love the picture, but had a screen issue (not burn in) 4.9 years in and was thankful I got a 5 year extended warranty - OLEDs are very susceptible to burn in - be careful.
The C2-77 is on sale at LG.com for $2500 - great price!
I have the Yamaha RX-3080 - it's pretty good for the price but a little underpowered for my large room - but the A2A should be OK in a small room.
Staying with 5.1 to start is good advice.
I would not buy low end Klipsch or any big-box surround speaker package.
Get a "proper" sub: SVS/REL etc and don't skimp on the center channel speaker!