- can Finale meet my requirements listed above?

Yes.

In fact, you will also be able to do stuff like only view the string section, or the wind section if you wanted.

- does Finale include the Garritan SoundFonts, or do I need to purchase those separately

They're not really "soundfonts", but Garritan Personal Orchestra sounds - essentially a virtual instrument (VSTi) of over 500 sounds.

They come with.

- will Finale/Garritan make typical downloadable MIDIs sound like your samples, or do I also need to find highly tailored MIDI source files?

A MIDI file does not make sound. It tells a synthesizer to make sound. The resulting sound depends on the quality of the synthesizer. In your case, that would be Garritan instruments. So any MIDI file you download and import will trigger Garritan to play (assuming you have it set up that way) and those will be the sounds you hear.

However, a word of caution: The MIDI files themselves will vary in quality depending on who made them. WILDLY. Most of the ones available at somewhere like IMSLP will be decent to very good.

But the person who makes the MIDI file may not have included things like dynamics, or expressive things, etc. Additionally, if they created their MIDI file on a different system, and/or different synthesizer, and they included patch information (which tells the synth what sound to use), the patches they chose could differ wildly from GPO. So their Flute may be patch #73 on their synth, but it's 22 on GPO. If this happens, you could expect to spend a great deal of time choosing instrument sounds and editing the file. This alone could actually be more trouble than it's worth.

Your absolute best bet would be to find NOTATION files actually done in Finale by people who not only notated the score correctly, but who did playback correctly in Garritan to begin with.

In the old days, some people used to make MIDI sequences and they'd write a 4/4 piece in 6/8 so that when someone opened it, if they tried to re-print it, it would be a lot of work to fix all the notation - it sounded fine but looked horrible - all kinds of extra dots and ties, etc. It was a sneaky way to "copyright" it - make it hard to do anything but listen to.

So MIDI sequences are totally hit and miss - if you download a sequence it may simply be raw note data and if you import it into Finale, it may look OK or it could be a mess. Starting with a Finale file instead, you stand a better chance of having less stuff to mess with to see and hear what you want.

- if the latter, where can I find/buy very high quality classical music source files?

Some other posters will have to help you here Barry. There are sites where people upload Finale files, but not everyone puts the same amount of work into their files - some people make it look great, but don't do a lot of work getting it to sound great, and others get it to sound great and don't worry about it looking so great. Additionally, it's not like there's some huge library of every piece on the planet - a lot of them are composing their own works, or putting up gospel arrangements, or whatever. So it really depends on what you want.

In some ways, you're almost better off to download a PDF score from IMSLP and listen to the piece on YT or buy the audio for it. I know you cant mute and solo instruments, but at least it is what it is - you get on with the business of listening and reading, without spending minutes to hours or days editing.

But if you really *NEED* to mute and solo instruments, Finale would be about as good a choice as any other DAW (Cubase, Logic, PT, Reaper, etc.). And it would be excellent if you can work from original Finale files.

Sibelius does this neat thing where only the staves you've clicked on will play when you press play - unselected staves are muted. I'm not sure if any more recent versions of Finale do this or not. Hopefully someone else can answer.

Good Luck

Wow! That was a superb response, more than I ever hoped for.

Thanks for spending the time clarifying this. I really appreciate it.