This setup is possible

PC---USB2--------------------------------------------+
|                                                                      | USB2 connection for
| USB3                                                             | operation of the unit via 2nd TM FX instance
|                                                                      | to be able to handle preamp gain, routing much easier
UFX+---ADAT1 OUT-------------------->ADAT1 IN---UFX (clock slave)
         \--ADAT1 IN<------------------>ADAT1 OUT---/

Optional with a 2nd ADAT connection to be able to route e.g. 16ch @single speed or 8ch @double speed.
You could even use the AES port which gives you two more channels no matter which sample rate.

On the UFX+ you can theoretically also save the routing in one of the 6 user profiles and use stand-alone operation.
But this I would only do if really needed and if you do not need to control mic gain.
You can do it also on the device, but with TM FX it is much easier and you can save/recall the setup in snapshots.
See manual chapter 23 about stand-alone operation.

Regarding TM FX. If both devices UFX+ and UFX are connected via USB, then you can control both devices via TM FX.
Either in one TM FX window, there is a selector field in the upper right corner, where you can switch between the devices.
Alternatively you can open a new / 2nd TM FX window, where you select in the one Windows the UFX+ and in the 2nd Window the UFX ("gen1").
Even the window position and sizes of both windows are being stored in workspaces.
So you can save the settings as workspace and also use the Workspace Quick select slots and easily recall certain typical srttings with ALT-1..ALT-9 ...

The better solution would be from an operational perspective to get UFX III and use MADI for extension and the work with RME connector with remote control capabilities for 12Mic, Octamic XTC or AVB Tool.