Will using solid strand wire(as opposed to multistrand traditionally used) to power the vtx and camera cause a any issues? The kind of wite used in the telecommunications industry? I have some and it is capable of a tight twist to prevent outside power influence.

As far as I know the only downside is flexibility, but it may be more susceptible to interference.
Twisted pairs for signal is good. Twisting the dc lines won't have any effect except possibly damping noise a smidge.

Solid core is brittle, don't use it.

Solid strand wire is more susceptible to fatigue breakage from vibrations. It also has lower ampacity compared to similar gauge stranded wire.