I'm planning on same combo of roof and R&R for my Kombi. Hilo roof booked in for October, then Reimo 3000 planned for new year.
My priorities are very similar to yours I think, young family so seating at the back (no rails) would be baaaad. Want the isofix option and properly crash tested for obvious reasons too. The Reimo seat was the only one that seemed viable for this particular combo of use cases that I found (apart from RIB which is too high with a Hilo).
Beware that the Variotech 300 does NOT lock for travel in the forward position in a SWB van. The variotech 3000 WILL lock in the forward position for travel but only if you get the more expensive bonded rail option (bolted rails only allow the positions adjacent to the bolts same as the 300).
The only major concern I have (barring the cost) is whether the roof height will be too low with the Hilo / 3000 combo as I've not managed to find anyone with the exact combination so far. Not a huge deal as it'll be kids in the back 99% of the time and they will be travelling in the forward position but would clearly be long term advantageous if the rearmost position was usable too.
*edit - didnt see this thread was from Feb.... ><!