Hi there,
We were in exactly the same position 6 months ago when we set out on our ground floor remodelling. We also started out thinking about doing the loft at the same time but decided that as its a very self contained project we would start with the ground floor, learn from our mistakes and then attempt the loft in a few years.
Having spoken to a number of design and build guys recommended on NVN we ended up going down the architect route thinking that the extra cost would be worth it as we'd end up with something special and potentially different (well as different as you get with a standard clapham terrace
).
We also hired an independent project manager who we had to let go before the build began but that's another story...
Our architect was by no means cheap and while I wouldn't say that our architect did a bad job I really haven't been particularly impressed. He didn't bring anything new or interesting to the table, all his ideas bar one we had been discussing with the design build guys or came directly from us via magazine cut outs etc. His one big idea was really rather impractical. He did have the grace to admit that this was the case when i pointed it out to him, but as the client i was hoping he would see issues and design solutions not the other way round.
If we were to do this again we would go down the build design route and i would not hire an independent project manager.
I should caveat all of the above by saying that we haven't started to build yet having been let down but we are now just about to start so ask me again in 6 months time
Best of luck with your project.