Re: first pcb stebs - sallen key filter
It's not clear if the available PCB technology allows for dual layer and if through-plated vias are available at all.
I agree with most comments about the present layout except what's said about impedance matching an signal reflections. These things are meaningless for a circuit with 5.5 MHz OPs. Although you didn't mention filter frequencies, it's pretty clear that it's no high speed circuit.
Circuit ground should be designed at least as a meshed net, power supply bypass capacitors near the OPs should be provided as well.
It's reasonable to place the filter components grouped according to the signal flow.
As you are using conventional capacitors and resistors, there's a fair chance to route the circuit as single sided PCB. It would be easier to use DIL OP packages.
P.S.: Seeing your latest post, did you actually decide about SMD versus conventional parts?