Alternator Sizing - Amp requirements

That's great!
Just a quick look at the pdf right now.
My interpretation is Denso's rates their alternators at 5000 rpm shaft speed as the lower line crosses 90 amps at that rpm. Less certain about this, but the lower line may be 12 or 12.5 Volts, hence the 12/90. Or maybe its showing the low end of the current output when controlled to 13.5 Volts.

The circuit diagram looks to me like a self feeding arrangement. F is an internal field connection and the smaller B is a smaller output connection feeding the F through the IC. I think S is the external field connection or start up.

There's guys here who are much better at reading circuits. maybe they can provide some more insight.
The circuit as drawn has some similarities to one commonly used with GM self-exciting alternators that requires an alternator lamp. Don't let that be a concern. That's just one of several ways they can be set up.
I haven't done more than glance at Denso regulation setup some time ago. I know AndyF and others have posted about the wiring connections. I just havent had a need to pay much attention to it.