First find out if the property can be perked for a new septic system as you may not have a system that's approved for anything other than a mobile as opposed to a permanent home.
Then be sure of your costs for the foundation and all other costs before you proceed. Then get the house placed and THEN add the garage. You may find out there are some unexpected costs involved and by spending the money for a garage before setting the house you may find yourself short.

As far as appreciation, yes, it will appreciate in value because it will be sitting on it's own land. Just not as greatly as a modular or a site built home.
And you will be able to get a regular mortgage just like a "normal" house.

Sounds like a good deal to me. Just be sure of the dealer and firm up all the costs before proceeding.