Re: One question only...
Kees et al - Virgil at "HF projects for radio amateurs" in the Old Glory has a relay switched filter board rated 100W for $90 as a kit. V used to offer a 50W compact filter with a rotary switch .. possibly still has the PCBs for it.
Fred at Far circuits can sell you the PCB for the filter from the Kossor 40W HF amp for $11 but with no other parts. Diz, AKA the toroid king in FL can make up the difference (Fred is pretty flexible and not US amateurs may be able to get him to ship the PCB to Diz and then Diz ships the whole works including Silver mica caps to you ). Fred May be able to sell you the rotary switch . If you want relay control you would have to build a daughter board to interface to the switch wire in points .
Fred also sells the 200W LPF filter board from the Sabin amp. That uses switched relays from a jejeune cct. Ie rotary switch switching one in at time.. There No default relay set ie if the switch is parked then the Tx sees an open cct. He has the relays to suit. He can send you out an excel spreadsheet of the LPF component settings.
There are plenty of "maybe dodgy" Russkies etc on Ebay offering stuff but whether it turns up once you have paid ??
Baruch Z, RF engineer in Israel may offer LPF sets to go with his super high power amps. (as in 2.2kW RF out S/state) . He does not seem to advertise them separately. https://www.ebay.com/str/4z4rb/ ie. what is inside those fully made up amp cabinets ?? But these Filter sets are of course overkill for the task at hand if they can be had.