There is a lot you can do with the build and there is a lot you might want to do yourself As someone already mentioned.... many of the items can be done after build and will cost less. Not to mention you will pay taxes on the cost of the house.
Yes, they will put something on the floor of the lanai. We opted out as we are doing something else with our lanai floors. We also opted out of the blinds and had 48 hour do that for us. I ordered them the same day we designed the home and he put them in the day of closing.
There will be a lot items you will want done with the build so you don't have to mess with it, but there will be a lot you will want to do after!
One of my girlfriends who lives in TV and hasn't closed yet, has started the process, so when she closes, the contractors will be in place. We on the other hand could only hire a couple of people and are doing much of it after moving. it. But it does seem to be going fast!
Also... Total cost will depend on how much you upgrade your lot.
Trust me.... it all works out in the end!