converting a Sprinter with Ikea "stuff"

A couple of other considerations - the Sprinters aren't square boxes, so you'd be dealing with curves to fit upper cabinets plus of course all the fittings in lower ones. Some high end B conversions from Canada are made with partly solid wood cabinetry custom fitted by Mennonite carpenters, and the work really holds up well - one reason they are pricey. Cheaper unit doors might begin to skew out of line.

I agree with John. Watch the weight and attachment.

I use IKEA LED lights in our Motor home. That is a good idea that you have, and will probably work, as IKEA's speciality is tiny homes and spaces. But be aware that much of their stuff is make of HEAVY fiberboard, whereas most RV stuff is built and designed to be lightweight. Things like hollow walls, cabinet floors that are thin panels with cardboard stiffners between, and other such. So just think light, because weight builds up very quickly.