That’s not going to be too hard. All you need to do is set the inputs up, if there’s anything beyond the 4 control channels (not sure what default glider set up for throttle is!) then you set them up there, give them a switch etc.
Rates, throws and expo is then done in the mixer screen for each channel, the expo is on the first half of the screen. Dual rates are done by duplicating an input in the inputs screen then changing the rate of the second input and assigning it a switch.
Painless 360 shows how to do this through OpenTX companion very well.
Once you work out the workflow for open TX it makes more sense. This is its downside, in a pre programmed, closed system radio there is a framework for you, with sub menus and labelled functions. Obviously you can’t then work outside the available limits, like some TX’s have only 3 mixes available, but they are easier to see when you start.