Welcome to the Zone.
I recognize your name from pirate, so as they would say, read up!
1) Are you looking to build or to buy?
building is cheaper but you will inherently have some things to work out. buying will cost more but you will get a reliable system from the start.
2) The plasma table will be easy enough to figure out what you want. Sift through the plasma forum and you will get a good idea of what you are looking for.
3) For the fancy carvings and such you will need a 4 axis machine. This will be a definate step up in complexity and cost compared to the plasma table. A commercial unit capable of 4 axis carving is pretty pricey. Check out this site for a look at what is needed for 4 axis column carving.
art ransom is the author of that site and he is a member here.
4) as far as putting them both together, you will have tradeoffs to make it work for both. it is a matter of wat will be acceptable to you and your dad. After you check out some examples of separate machines you will be able to decide if you think you will be happy with a combo machine.
Shopbot is a pretty nice setup and they have a setup that would work for your combo machine. Here are the standard 3 axis routers, which you could use for your plasma and any flat wood work with a router attached.
then for the 4th axis for the columns you could bolt this on and go to town.
5) your autocad drawings will be adequate for your parts. You will need a dxf for most 2d parts which will be opened up with a CAM software. sheetcam would be good for plasma and is cheap. Surfcam, Visual Mill or others capable of 4 axis stuff will be pricier.
The CAM software generates the code needed for the controller, which actually tells the machine where to go.
Everything you need to know is here, it just takes time to read up and digest it all.