Does anyone have advice for a total novice (old but always had
baseboard heat) on the subject of the filters that go behind the
intake registers for a gas forced air furnace. For example:

Disposable versus Permanent?

Disposable 30-Day versus Disposable 90-Day?

How seriously to take the 30-Day and 90-Day limits?

MERV 11 versus MERV 8 versus MERV 4?

Permanent with polyester (claimed to be hard to wash) versus
without polyester (more expensive and claimed to be hard to wash)?

Suppliers that have good prices?

Thanks for any help.