I grew some Coleus from seed and now they are about 3" tall in a small pots on my porch. Can I move it to an indoor pot and just make it a houseplant?

Also, can I keep one or two on my porch until late fall, and then move them somewhere inside to overwinter?

Yes, just be prepared to offer a little more sun for winter than summer. I wouldn't leave any outside once it gets under about 45 degrees. Cold really freaks Coleus out.

Coleus can be grown indoors, but they do tend to languish during the shorter days of winter. They need regular pruning back to keep the stems from becoming leggy. Of course, they will require being on a very sunny windowsill where they get direct sunlight for most of the day. If you cannot provide that, then it is best to treat your Coleus as an annual.