I bought a 2007 170 sprinter in Dec. of 2017, I'm just getting to paneling the walls, I have not experience or even a proper place to build, no garage, I have to keep everything in my van. My biggest mistake so far, was not checking the side trim panels for leaks, had to stop pull lower 1/3 of wall out and rebuild. Most of my time is gathering and learning how to do the phase, which always starts out slow and confused, by the end I'm moving at a good clip and I still always think the next phase is going to be sooo easy, which is never has, not one part of this process has been easy, all of it worth it but hard. As for electrical, when I started I thought I needed to do a full build, what I ended up doing was the basic DC wiring and using a harbor freight battery charger as the power source, over time I've slowly built up electrical components, now I'm at a Battle Born 12v 100 amp, inverter, battery monitor with NOCO G15000 charger to charge it.
Point is, if I can do it you can too, it will be hard, theres a lot of resource out there, if you want to do it, you can do it.