The only limit I'm aware of any of the favorite menus is with Styles list. It is limited to 150 but it is also the only one with save and load features and is a powerful benefit to narrowing down Style searches. The instrument favorites don't reference a limit in their help file. Recently used instruments are inserted into the list automatically so if there's a limit, it's more than 1110 because what is currently display in my Recently used list. If there's a limit, I assume the oldest in the list is overwritten with the new recently used files once that limit is reached.
I believe the instrument favorites do stay selected for years unless they are intentionally deleted and overwritten. I use the instruments favorites on a per project basis because they link to styles so it's easy to find similar styles that use the same instrument which is a valuable resource for making MultiStyles, which I also use a lot. I usually erase the existing favorites when I start a new project so the list is synced with the current project.

In the MultiPicker, currently clicking a track once selects it and clicking it twice either initiates playing the file demo or playing the instrument using the Chord Sheet. It may be easy to select a favorite by giving up one of the double click options but it seems logical to have play functions rather than mark a favorite. The current Favorites feature marks the track as a favorite and give access to five other functions including displaying a list of similar RealTracks and Styles that use the selected RealTrack. I prefer the more versatile and robust current Favorites over this wishlist request as it's described at the moment.

BIAB 2025:RB 2025, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.