Not a volt nut, and again, pick a connector if you prefer it for the purpose. Its just copper at this point, It could be 5x5mm copper pads if you would prefer to spot weld copper - copper if you really want to keep to the same metals
Ok, So I read that thread slightly differently, Strain / Stress is not a resulting factor, more the better the thermal isolation of the regulator the hotter the leads meaning any thermal gradients are amplified, so doesn't really rule out slots, just means top focus is that the zener pins are the exact same temperature, so high thermal mass would actually benefit the LM399, the faster heat is sunk from the part, the lower the gradient at the cost of power consumption
So I'll revise him
On to Kleinstein,
I've checked a number of cheap PCB vendors and there minimum silkscreen thickness means what you see is what you would get, a line of solder mask separating the guard trace from the SOIC pins, does that make things easier for you, or still not quite, I'm too used to soldering wire strands to MSOP pins, So I'm not the best general reference for what is or is not easy to solder.
I'd prefer to not rotate the integrator op amps, as the other orientation makes other parts harder to route, what exact parameter are you trying to work by minimizing that node to such an extent?
There will be lots of room left on the PCB, its bigger than 50 x 50mm, and not a good shape for 50 x 100mm, meaning work on a maximum of 100 x 100mm which leaves tonnes of room. This is why I hold no issue with adding connectors, Big through hole test points, or alternative footprints,
Planning the middle left to be AVR and bottom left power supplies, leaving almost the entire right side to input