It's very easy and tempting to go down the rabit hole with this.. there's a lot of crap people will have you believe you need to bring or install.
After I bought my Grenadier, which already had the roof conversion done, I worked with Expedition Centre (Sydney) do an internal fitout. But I really focused on what for me are the most important functional things. This is based on living out of the Grenadier for extended periods and being able to travel and work remote: 240V electrical setup (incl. OEM battery box replacement to significantly reduce weight and make access easier), water setup, storage, induction cooker, compressor, and UHF. This allows me to be fully off-grid, run starlink, work on my laptop, shower and so on. Other than this stuff, I've got a single tub/box with recovery gear and some tools etc.
Everything else I keep super simple and as lightweight as possible; fewer things to pack, unpack, service, repair, clean, and so on. Everything in my Grenadier I can access without having to move other things to the side. Nice and simple.
Expedition Centre have done a few Grenadier roof conversions now and several fitouts, so they know what they're working with. It's an investment, but high quality (custom) work that will be worth it if you use your Grenadier that way.