You can get a lighter set-up by using an iPad instead of the computer
This is what I have done
XpressO for the acoustic sounds and iPad for Synth Sounds (even if the XpressO has a Analog Modeling Sound engine
There are some very nice apps for the iPad (Thor Synth, MiniMoog, Nave to name some...) In combination with Audiobus 3
I use the iPad also with NewZik which allow me to read the Music Sheets
It should work and it is very light to move and all can be powered by Power bank (XpressO, iPad and if like me you have a pair of BOSE S1 Pro they are also powered by batteries so. (they also have 3 inputs so and integrated mixer so no need for additional mixer
Do you know that you can also put you Backing tracks in the XpressO and trigger them by notes or footswitch there are many different solutions