I waited a couple of days, hoping you'd get a few more suggestions, finally started typing and then get myself ninja'd.
I have an SPCycle G028 that I've built up for bike-packing / light-ish touring. I've fitted a rear rack, Bluemels Basic mudguards (a pain to fit) and GRX 820 2x mechanical - 48-31 chain rings and an 11-36 Goldix cassette.
The frame is a little more aggressive than your Velobuild, but probably solvable with the right stem and bars combo. It's also very heavy: 1305g for a Large/56, painted and with accessory bolts, without hangers, and 498g for the forks. So quite a lot heavier than advertised.
It has down tube storage (find your own bag) which I can fit a multi tool and BBB Doubleshot pump in, but spare tubes, patches, basic first aid kit have to go elsewhere. It has quite the array of accessory points/rivnuts, though you'll need to get creative to fit full-size mudguards and a rack. Routing 2x mechanical outers and hoses wasn't too bad - I have separate bar and stem, routing hoses externally to these.
My intended use is 70% road, 30% off - basically the UK's National Cycle Network. I'm running Caracal 45's on 25mm internal width wheels; and hope to avoid mud. 🙂 The G028 gives plenty of room for these plus the mudguards.
For winching up hills fully loaded it's overgeared so I've ordered but not yet fitted a replacement 11-39 cassette which should work ok with GRX. I'd also go 46-30 if I had my time again, and may yet change here too.
On the road it's very stable, very unexciting and it's perfectly capable for gravel /unpaved bike paths. As a load carrier it's pretty good with around 12kg on the rear, 3kg up front, plus my 82kg, but I wouldn't trust much larger loads to the seat-stay rivnuts, particularly on rougher ground.
