LLC or subchapter S would also work. I used to sub contract through a company that did that, so they contracted me out and their contract with the client was between them and the client. I had no liability in it at all as all contracts were between parent company and myself.
In the end, it was not worth my time and hassle as there are always dicks out there that want everything for free. Private practice doctors were some of my worst clients, and they were absolutely clueless. When I would bring things up like HIPPA standards they would look at me like a deer in head lights.
If you want my opinion, the least hassle will be building them and selling them, but that will yield the least amount of money. The most money will be in what they call, "Professional Services." Which would install server set up, data migration, network services set up, and consulting.
I would just use your personal contacts and see how it works out before you decide to drop the money to become a LLC. Plus when you become a LLC expect the IRS to audit you the first couple of years since you are a brand new business. Then you have to get all your tax documents in order and so forth.
It is a lot of work for sometimes the biggest head aches you will ever get.