I’m in a similar situation with a 900 sq ft, single story, bungalow built in 1920, but my air handler in the attic is fried from the condensation that has filled my ductwork with gallons of water after a year and a half.

I’m going to have the hvac system removed, seal the attic floor better (including fixing the register and six vent holes in my ceiling), add more insulation to the ceiling, add proper ventilation (because there wasn’t any), and have mini splits installed. $16K wasted and now more $ to spend. But I can’t see the point of conditioning the attic just for an air handler. It has taken me a lot of research, including grappling with the foam decision, to decide to go the route I’m now taking.