Each Megaton House Theme is 1414 caps, but it is less with a good barter skill.
Skill books, clothing and other items appearing in themes can't be respawned by reloading the theme.
The house/suite can be decorated by placing items around the house.
If you defuse the bomb in Megaton, then talk to Tenpenny, you can access the Tenpenny Tower suite via the door on the balcony. If you do so, Godfrey will have talk options for all of the improvements you have in your Megaton house, even though they won't be in the suite. Also, you will be able to put all of your bobbleheads in the collector's stand so they will be at both locations.