I don't have the digital toolkit so I can't comment on that.
How many core rulebooks you need depends on how much reading and research you want your players doing between sessions. I might recommend that everyone have a PDF of the core rulebook available, but that only one physical copy of the book is necessary. (Maybe even zero, if you're comfortable with PDFs.)
One of the great things about PDFs is that they are searchable. Ctrl-F will save you
so much time. I'll be honest, a PDF is not my favorite way to
read a rulebook, but it is by far my favorite way to look up rules.
3-4 players is actually pretty perfect, especially if you're just getting started. Let the players choose their character types so that they can pick something fun and engaging. If they're not feeling picky, here's a reasonable breakdown of characters/responsibilities
1. Street Samurai / physical adept ("Meat")
2. Mage / Shaman ("Magic")
3. Decker / Technomancer ("Matrix")
4. Face (no clever m- alliteration here, "mingle"?)
Many first-time players and GMs find that Matrix is the most challenging to integrate into a game, so I might save that for last if it's an option. But if you have a player that's eager to try it then I'd say it's worth the effort to support them in what they want to play.
If the group hasn't tried out the system yet, the Quick-Start rules can be a good place to get acquainted with the world and the basic gameplay mechanics:
http://cdn.shadowruntabletop.com/wp-content/uploads/2013/02/E-CAT27QSR_SR5-Quick-Start-Rules.pdfAnother approach is to start with a rules-lite approach - the recently released
Shadowrun: Anarchy - before making the leap to the more mechanically-oriented 5th Edition. This depends on how much detail your players enjoy versus how much time they want to spend just telling a story together.
But the most important piece of advice is to have fun. Shadowrun has a steep learning curve so don't expect everything to go perfectly from the beginning. Wing it as you learn, and keep things moving. Nothing kills the fun like digging into the rulebooks for 15 minutes to research the exact answer. Make a reasonable guess and move on and you'll do well.