Hi, and thanks for your comments!
Yes, I use Musescore 3. Alas, that's the only version that runs on my PC, so switching to more advanced applications is not an option at the moment. It's very cumbersome to add articulations and such this way (like playing around with those hidden tempo changes); there is, in fact, a plugin for changing the note duration, but one has to set each note separately, which is an awful lot of work. I really don't know what other options I have in MS 3.
Most of the fugue was worked out on paper in an SATB open score format with no particular instruments in my mind (I chose those strings for the audio rendition because that soundfont is amongst the least horrible I have). Actually, what you suggest is a very good idea! One thing that makes me think is what role to give the double bass before the dominant pedal. Supporting the cello throughout might be a bit too much sometimes.
Yes, exactly, those form the kernel of the episodes.