The UHKs use OEM profile keycaps. If you want caps that can be used on any row without a height/angle difference, you’ll have to use a flat/uniform profile. That’s something you’d need to get from a third party, as UHK only sells the OEM profile.
Here’s a tool you can use to see a side profile of some of the common keycap profiles.
Finding compatible caps is quite a challenge, but luckily there’s a couple of custom keycap services that provide such profiles. Yuzu and FK Custom are quite good quality, and I’ve made a few sets from them. They have some UHK templates to make things easy, or you can custom design the legends to be whatever you want if you’d like. You can also make a bunch of extras with your order, if you can’t make up your mind 
.
There’s also Thockfactory, but I haven’t tried them yet. Iirc, they don’t offer a uniform profile, but they are customizable. So if you know for sure what you want on your legends, and you don’t plan to move them around, that’s another option.
Yuzu keycaps are opaque, so the legends won’t be illuminated. The FK Customs are available in a shine-through variant. If you think that’s something you’d be interested in, I’d check out their Discord channels, as they are very friendly, and someone will answer your questions pretty quickly. You can also ask here, of course. 
I prefer flat profiles myself, and here’s some I’ve ordered from Yuzu, and FK:
My FK Custom caps (XDA profile):
My most recent Yuzu caps (KAM profile):
Here’s a blog post from @maexxx showing off just how intricate and complex the Yuzu customization can be:
Anyway, my suggestion is to take your time, and experiment with your layout before making any decisions.
As for the wireless connectivity-
Have you tried connecting to anything via Bluetooth? (no dongle needed for BT) Dongle is definitely more stable, but like I mentioned earlier, BT should currently work fine if you’re only using one BLE device.