I'm not the expert, but I do read a lot, so this is coming from "book-larning" and Ravelry rather than personal experience.
* don't mix yarns of different fibre types unless you know what you are doing as they will behave differently when the fabric is fulled
* warp yarns need to pass the "pop test" : does the yarn "snap" when you break it, or pull / drift apart very easily?
* rigid heddle puts less strain on the warp than a multi-shaft
* as well as tension, warp gets a lot of friction during dressing and weaving, so warp yarns should be able to withstand friction as well as tension
* warp yarns which cling to each other make it very difficult, especially for a novice, and especially if there is not an enormous amount of tension. (So a pure Shetland jumper yarn as the warp on a rigid heddle might be a bit of a challenge, for instance)
So for me, unless your yarns don't pass the pop test, I'd be inclined to go to with using all handspun. Otherwise, or to eke it out more, find commercial yarns of a similar constitution (fibre type and proportion) for the warp.
I know the temptation is to not sample because "it's a waste of my precious handspun" - but it's more of a waste to weave the whole thing then find the plain weave has swallowed all the vibrancy of the glorious weft
(I watched a friend discover this. Heartbreaking
)