We installed an aftermarket digital dash, because that was what my son wanted.

The Hot Wire kit provides wires in the harness for the gauges. You use as many as you want, or as few as you want.
We simply changed the sending unit for the water temp to match up with the gauge we used.
Oil pressure gauge on the car was mechanical, we added a "T" so we could use the stuff to attach to the OP gauge and retain the connection for the computer matching op sending unit. I see no reason you couldn't switch the mechanical set up we used with a different op sender to match your OP gauge.
Fuel gauge was unaffected. The Hot Wire harness does provide a power wire for the fuel pump through the ASD relay.
I suspect you will have to do a digital speedo or come up with a way to get the mechanical speedo to work from the digital input.

Have you checked on the Hot Wire website yet? They are very good at what they do, they can answer all your questions. Since they are building a harness to your specs, they may be able to accommodate some of the stuff you already have. One of the questions they asked was which trans were we using. Gene