So I have spoken to a few dApp development companies, and here is what I have taken away from it:

- To start, it's going to be Bitcoin (on the lightning network) and native Monero.

- The off-chain orderbook is a no-go. Customers will be more likely to trust a dApp powered by contracts they can see on the blockchain.

- It's cheaper to make a browser extension than it is to make a desktop application, so the Fornash DEX will be a browser extension.

- It's going to support limit orders and market orders, with bi-directional atomic swaps.

- Basically the same UI/UX as Uniswap V1.

Of the three companies I interviewed, LimeChain (limechain.tech) was by far the most impressive. They said they will have a quote for me some time next week. I'll post here again after I next speak with them.