How to add panels to a system when existing panel no longer made

You should be able to "go over" the MPPT controller "max panel wattage" rating... But your controller will "clip" the solar array available power to max rated charging current/voltage to the battery bank.

Over paneling MPPT controllers is common. But if you need to support a larger array, then either getting a new/higher rated output current controller or using 2 or more controllers in parallel charging the same battery bank are the two solutions. Either solution (new controller, or 2 or more controllers in parallel) is fine. And the two controllers do not have to "match"--They can be different size, brand, models. Each will charge the battery bank as it is programmed.

The details matter. What are the Vmp/Imp ratings for the various panels? Yes you can "mix" different panels on the same array--But there are rules to follow and sometimes, if the specifications are too far apart (i.e., 10% or less miss-match of Imp for series, and Vmp for parallel wired strings), one cannot make an "optimal" match...

I am not "big" on picking panels with "battery shade" performance... From what I have seen, running a solar panel in shade will, at best, give you about 5% of its normal direct sun output power (for me that was what I saw as blue sky back scatter to my array when shaded by trees towards the end of day)... If you get a "better shade tolerant" panel, maybe 6% harvest instead?

Shade is a "killer" for solar electric power. Even a little bit of shading on a large solar array (such as utility power line shadows on array) can kill upwards of 50% of harvest until the shade moves off panels (as sun arcs across the sky).

For a basic first assumption, if your array is "in partial or full shade" for 1/2 the day, then assume the system will only produce 1/2 the expected energy during that day. And as the sun moves across the sky between summer and winter, so will your shading move/charge too.

For most people with shading issues, as winter approaches, shading from trees/mountains/etc. becomes worse. If you have the choice--Installing the array 100 to 100's of feet away from your cabins is usually the only practical solution. And installing arrays farther away requires larger copper cables (to keep voltage drop down) and usually a higher voltage array (high voltage => lower current and lower voltage drop). But that usually requires purchasing MPPT solar charge controllers with higher input voltage ratings (i.e., a 150 Vpanel-max rating vs 100 Vpanel-max rating... And there are some that have 600 Vpanel-max input rating--All of which usually cost more money).

-Bill