1' on center may be pushing it for the floor depending on where you live. How are you heating the rest of the house? radiant floor as well? Have you done a heat loss analysis?
There are lots of gas-fired boilers that will work with your system. For the a/c, you'll need to decide if you want to go with a split system, high velocity system, or a traditional ducted system. They all have advantages and limitations. A split system is easier to zone, if that is a factor. A high velocity system is easier to retrofit since the ducts are very small. A traditional system is less expensive.
You should have plenty of power, unless you have something unusual with heavy loads in your house.