In order to assist the threadstarter with his back yard construction project.
Make it a single. Unless you have someone to reliably and consistently pay the bills and want to scale the whole thing up to account for the lost payload.
As the target design altitude increases so will the tr thrust/mr thrust ratio, unless you really enjoy directional challenge.
Make the engine big. The higher the intended alt. The larger the "size"of the gas producer to the lonely power turbine(s). Make it torque out first, sooo much more intuitive and linear for judging your power situation. Even if it means pushing more fuel drums around.
As much as it is a safety feature it is a psychological salesmanship feature. That is...make the cabin small in relationship to the installed power and the size of the rotor disk. Everyone will be consistently amazed when it is loaded to the headliner with junk and full of fuel and "always flies away" Brings in more money with a second trip at lower elevations. Otherwise it gets really tiring explaining why only 30% of the seats can be filled. Hard on a girls reputation too especially if she is made by Bell.
Lock number / control cross coupling concerns, I am willing to bet aren't a problem this planet. We could ask VF about this. Fly by wire parts are found in the electrical section of the hardware store however.
On a side note, protecting the dignity of the Bell ladies. The 206L4 ha t/r, 417(eagle 407 hp) and 214b I am confident would happily keep up with the beloved ecureil b3. Though on a design note it is interesting to watch a spec. L4 walk away from a spec. 407 above 8000' pa ISA +20.
Hope this helps. Send pictures.