If all you need to do is change Presets then no, you don't need UNO. I do, however, recommend getting the UNO_ControlCenter Editor. It works with UNO AND the stock Chip. If you want to, say, turn ON/OFF devices (OD, Fuzz, Delay, Reverb, etc) then get the UNO Chip.
You're using two physical devices. You'll want them receiving PC (Program Change = PC) messages on 2 different MIDI Channels.
Likewise, Expression pedal info (Wah, Volume, Delay time, etc). You can assign one Expression pedal to each device, or both to one, and do so per FCB preset, by using separate MIDI Channels, and unlike the ON/OFF controllers, you can change the MIDI Channels per FCB Preset.
With UNO you'll have 5 ON/OFF buttons in each FCB Bank. They'll send the same 5 CC (Continuous Controller messages) on the same 2 MIDI Channels, in every FCB bank.
Each ON/OFF button can send 2 different CC messages, on separate MIDI Channels. But they'll be the same messages on the same channels in every bank.
Those are just a few examples things to think about.
You're wanting to do a LOT.
You'll need to be specific about EXACTLY what you want to be able to do, and you'll need an in-depth understanding of how GR5 and the GR9 work.
If you search recent threads on using GR5, I've provided in depth instructions and a UNO_ControlCenter (Editor) sysex for use with GR5.
Once you've read up on it and tried the provided sysex, I'll be happy to answer specific questions
I know bupkus about the GR9.
You mentioned being a Computer Pro. When I worked in that field I made good money, and music was a hobby.
If this describes your situation, then I recommend that you dump the FCB for a Line6 Helix (best Multi-fx + MIDI implementation). The Helix is very capable of controlling the GR9, probably better than the FCB, even with UNO, and you can put the GR9 in a Helix FX loop, thus integrating the whole system. It also sounds MUCH better (and has better support) than GR5, and eliminates the fragile computer from the live performance scenario.