You can use the 15" deep Ikea cabinets and build out the back wall.

Or use 12" deep wall cabinets of any brand and pull them out to whatever depth you want.

Consider J&K....you can increase a wall cabinet to 18" deep or any depth. I don't think they offer a full height base door in 18" wide.

Appreciate that, would love to get it a little deeper than 15” just not quite usable enough for AV equipment etc. really hoping for that 18-20 sweet spot

RTA Barker and Conestoga both offer quality cabinets in custom sizing and have a wide variety of door styles.

Scherr's will make whatever depth cabinet you decide you want with the finish that you specify. I've used them and they are great to work with. Their product is excellent. Their customer service was outstanding. Not a troll, but I was really pleased with my experience and the outcome.

Spoke to scherrs and they aren’t doing custom at the moment due to the backlog…

That's too bad. Your other option will be to find a local custom shop. Then, get in line to wait. Most custom shops are price competitive.

Your fireplace is beautiful and I love the balance of the open shelving. Is it possible to keep the equipment in the lower cabinets? Or at least keep some open shelving. It might look very visually solid with doors all the way up

Vanity cabinets are 21” or 18” deep, and used quite often where reduced depth is needed, and you do not want to pay for customized depth. However, you have to be in at least a semi custom level of quality for a line to offer any real selection of options in vanities. Not RTA level.

Most stock lines only offer set pre made setups in predetermined stock sizes. Mid grade and up allow you to choose full height doors, drawer bases, or door and drawer combos, in any number of 3” increment sizes. So you can do 2 24” drawer bases flanking a 30 full height door base in the center, or any number of combinations. Work with a local kitchen and bath shop. But get RTA out of your mind for this.

Thanks verbo - helpful, do you happen to know any vanity cabinet manufacturers that also offer a slim shaker option?

You’re asking about a custom level quality product now. Omega does slim shaker quite well. But you are light years away from anything RTA price wise. And for sure, quality wise. It all depends on your budget. I don’t think you want to be spending 10K for this project, or you’d have started there, with a local quality custom maker, and it would already be done.

Conestoga Cabinets would be able to create this in the exact dimensions you need. They have many sellers for their products out there.