sure it would retain enough heat for baking bread, roasting meat, etc. I absolutely loved it (moved a few years back). I did it all DIY. Forno Bravo is a great place to start. They have tons of people who have made them with a bunch of photos to get ideas from as well as different plans. It took me about 4 weekends.

I now have one of the new portable pizza ovens (ooni). It's good, but not the same.

It would be pretty cost-prohibitive to hire someone to do it. I did it all myself and it still cost me > $1500. It was large and I used full refractory materials to insulate (it would hold > 400 degrees after 24 hours with a door on) and the outside never even got hot. You probably could build it for around half of that if you were careful and didn't try to make it "perfect".

You need a good foundation. Then you can create the base and main platform at the same time. Building the dome using firebrick isn't nearly as hard as some make it out for. Then all the finishing work is a bit of a pain, especially if you haven't done it before.