Gas and Oil Home Heating Furnaces - Old house, installing new furnace (LP) Help!

My house is a 1200sq ft, 2 story built in the 40's. Simple rectangle design on a crawl and a small area to stand(currently holds water heaters and water tank). Original heat source has been a propane fed space heater. worked fine and really did heat the whole house. now there is a little one in our life and the space heater had to go due to safety. My question is, if i were to heat only the lower level with 6 runs, can i asume the upper level will heat as it did before? and, cold air return placement? does it need to go upstairs, or can I put it up high on the lower level? Planning on a high eff. propane furnace. what size? dont know yet. have had home depot rep out and quoted me $11,000.00 for entire system. yes, eleven thousand dollars. i'm thinking more along the lines of under 2.5k doing it myself. any pointers are appreciated. thanks

That's alot of work and if not done right can be dangerous. I'd get a few quotes from independent dealers. HD subs the work out and it gets marked up so that they can make a buck off of it. Have them do a load calculation also.

first mistake was calling home depot

get some quotes from independant contractors

please do not do this yourself, too many variables that could trip you up

Thanks for the replies guys. you just bought me some free time with my new girl, but cost me some bucks. Time and safety is more important. I have had a few people in that do hvac work and have told me how many runs i would need and where they should go. is that something i can do myself as this is the most labor intensive and costly part. or could i potentialy mess up air flow if runs arn't layed out right? I'm thinking flex ductwork, as i have limited crawl space with big beams in the way, and let the pros do the main run and furnace/vent installation. any advice, or should i leave the whole job to the experts? i've done everything else to the house, just no experience with hvac.