Make your PI matching circuit heavy on the Cs and light on the L, so any PCB parasitic does not cause major mistuning.
And go for low-Q, so you don't need precision or adjustable components.
What is low-Q? Given the circuit functions in a 50 ohm network, having Z(L) = Z(C) = 50 ohms would definitely be low-Q. Having Z(L) = Z(C)= 5,000 ohms would be high-Q. I'd pick a Q of 10, thus your 3dB points will be +_5% of carrier. This may require careful selection/measurement of values. Thus Q=3 is easier for you.
Regarding stitching, for serious isolation use 2 rows of stitching to restrain the circulating currents right in those vias.