I was anticipating commercial registration and insurance would likely be involved,
If you're going down that road, it's a whole different discussion. You'll need an operating certificate, and the supporting manuals and systems for your organization, and yes, insurance will change. You'll need a pilot who's entitled to train pilots on type. There's some cost and responsibility to that.
DA42’s (maybe less worry due to FADEC nannies protecting the engines)
Yeah, Diamond installed that system so the owner would not feel the need to ride around right seat
Once the rental pilot is paying for a twin correctly operated within a commercial operating system system, they will want to take the plane as they wish.
Alex, you seem to be sidestepping some wise and
very experienced thoughts here, the advice is free, and trust me, way more valuable to you than that!
In the mean time, speaking as a pilot whose flown right seat to a less experienced pilots lots, If you are not confident that the rental pilot will remember the gear, and not shock cool your engines, you simply should not let them fly your plane. You either trust that the pilot is diligent, or you do not, there is no middle ground on this. Sure, we have all had to build experience, but some things are basic care and control considerations, and a pilot attitude, rather than an experience based skill. I have found, and state to a couple of owners that they were not caring adequately to their airplane while they were flying left seat to me.
And, worst, if the "rental" pilot left seat gets it wrong while you're right seat, perhaps being more bold, confident that you'll fix it. You may be in for a miserable, life threatening situation.
20 some years ago, an owner chose to ride right seat to me in his 172, while I flight tested the plane for a modification he had installed. The flight went very well, through to completion of the regulatory portion I was there to fly. The right seat owner mentioned in passing that neither he, nor the plane had flown in six months prior to this flight, and, he would be checking out three of his colleague pilots for spring operations next week (it was a commercial plane). I surmised, and confirmed by asking, that he had not flown in six months either. "Hey, perhaps you should fly a few circuits from the right, while I'm here..." He seemed reluctant, but agreed that it would be good idea. His first two circuits were poor, and the third landing I took away from him to save the plane from damage. This pilot was not up to flying from the right, much less correcting someone else's errors from that side! I've been the experienced pilot right seat in some really unwanted circumstances, it's not as easy as it sounds....
I’ve been considering renting out my twin for some extra spending cash towards avionics.
Alex, no matter which way you cut it, the lowest cost to you for the avionics you want, will just be to save your own money, and buy them without renting out your plane. I have owned planes since 1986, and never considered renting one out. It is my opinion that it is just not worth the hassle and risk for the small return.