You, my friend, are about to embark upon that most nonsensical of journeys--the endless and very expensive trek towards a “cheap” bike re-build. (After all the frame is free right? Or at least, you paid for it so long ago it seems free .... )
First off, 126 mm rear dropout spacing means you either have to stretch/bend the frame (Sheldon Brown will show you how) or use a 7- or 8-speed freewheel (Shimano makes good 7-speeeds, Evo and Sunlite and SunRun (Chinese nobodies) make 8-speed—should be about $15.)
The gear spacing on these clusters (Not cassettes) are odd so you might find some indexed shifters don’t agree with them. They will work, but not smoothly. Good news is you can get a ShiftMate for about $40 to even the cable pulls. See how cheap this all could be already?
Best if your brifters are designed for the same number of gears as the cluster—and 7-speed brifters can be tough to find. Microshift sells them new for about $60, and you can occasionally find rebuildable Shimano RSX shifters (used) on Ebay for about the same. 8-speed is easier to find, and costs about the same if you shop around. Under $100 for sure unless you get impatient.
I’d recommend looking for 8-speed 105 or Tiagra stuff—durable and reliable if you buy used.
Any front derailleur should be compatible with the brifters except maybe some Shimano MTB derailleurs—plenty of documentation available online. So, stick with NOS or used 48-38-28 chainrings, I’d say—should be good enough for short tours and cyclocross also.
I know from experience the Shimano road FDs can handle old-school Shimano MTB chainsets—don’t know about newer ones, but there is a lot of info on the Internet about it.
Of course, you can always spend another $40 on a front ShiftMate.
You will probably want an MTB rear derailleur so you can run 11-34 or 11-36 in back. Up to 9-speed all Shimano RDs should work with all brifters.
—Or——
Spread the frame in back to 130 for road or 135 mm for MTB hubs, and you can run all the latest gear—cassettes and freehubs instead of clusters and freewheels—And at 135 can use the strong MTB hubs.
I definitely recommend this for steel frames—so many more options in wheels, tires, hubs, cassettes—drivetrains in general .... Just be sure to look up the various cable pulls for the various derailleurs. (
Cable Travel Adapter Cribsheet Ordering from Peter White Cycles )
So ... cassette, crankset, derailleurs, brifters, maybe a ShiftMate ... by the time this Bianchi hits the road you will have invested so much money and so much of yourself you will almost completely refuse to consider the very common-sense suggestion that you could have sold the Bianchi and the
cash from that, plus what you spent building it, would have paid for a brand new bike which you already would have been riding for several weeks.
Been there, done that, in the midst of still doing it again and again.
You decide.