You'd be surprised! It also depends on how in-depth you want to go: A screwdriver and a couple wrenches will allow you to do 90% of basic repairs, like adjusting cables or attaching water bottles. Do you want to get into bearing adjustment--hubs, bottom bracket (the crankset axle), headset (the steering bearings)? Then you'll need more specialized tools.

Once you get a few of those "obsolete" manuals, and educated yourself a little, then you can determine just how heavy or light you want to get into repairs.