I would be diving with a single tank, doing no deco, and looking at a dive that's...at most...half of what you mentioned.
Scapa Flow Diving
This page wouldn't pull up for me last night. It looks like they don't even consider letting people dive in wetsuits.
I've got no interest in a drysuit at this point, so I guess this is a no go for me. If I change my mind, I would consider ordering from them. As you said...with the conversion rate, the price would be pretty good.
Looking on Scapa Scubas website...it sounds like they have dives setup for all skill levels.
That and define "interesting." A good chunk of my dives have been in local quarries. Just about anything I could possibly see would be more interesting than the scenery on a good amount of my dives.
I'm looking one year out (summer of 2020). If I decide to go, I would be booking well in advance.
Scapa Scuba run courses and diving in general in Orkney. There are enough shore and easy sites to do that. However, what people really go there for is the remaining German Fleet. You can do some of that on a single but you would be missing out. Unless you take a whole boat you will be quite limited using a single for some dives. Everyone else will be definitely diving the big 7 wrecks, if you don’t want to dive an upside down battleship in 44m (keel at 20) they will leave you on the boat. You might do a single plus a pony but really a twinset is ideal.
One way to get a space is to keep an eye on FB pages such as
UK Dive Spaces Offered/Wanted Public Group | Facebook or the boat’s ‘Friends’ pages eg
Friends of MV Valkyrie Public Group | Facebook
These boats seem to be best regarded:
Award winning Orkney diving charter Scapa Flow, Shetland and Norway. Two boats, run by women, very comfortable. I have dived from both.
Halton Charters – Scotland and Norway Liveaboard Dive Charter Run by a bloke, accommodation more basic.
Home Run by a woman, newly built, very shiny, accommodation is a self catering house by the harbour.
There are several other boats but I’ve not been on them at all, they have seen less investment I think.
You can rent cylinders, (3l, 12l, 15l steels, 7l, 11l Ali stages), twin 12s (but bring your own bpw). Lead and air are free, Nitrox, trimix are available.
Food is usually priced separately. Cost is about £700 for the boat, £150 ish for food and then gas can add up if you get fresh best mix fills every dive.
I don’t think anyone would stop you diving a wetsuit. That is not how U.K. diving works. The skippers are transport, if they give advice it is because they are actually convinced you will very likely die otherwise. That is not to say they will not take the mick constantly.
I have a couple of club members who only have wetsuits and who I would be reasonably relaxed about doing Scapa, however they already do similar diving here. I did have someone wimp out on a recent Welsh trip though, diving in a wetsuit for one day and then switching to a drysuit.
If you fancy an easier taste of U.K. diving then places like Newquay, the Sound of Mull, St Abbs, all have excellent diving. Not so intensely historical but good all the same. It is significantly warmer further south too.