Nice tank! I would position based on what I wanted to do with it. If grilling is your main forte, flat. If you lean more toward smoking, then upright! Either way, this will make a nice build. I am looking forwarded to seeing it grow.
On getting the smell out, it will always burn out. Diesel is easier, but propane cleans up good too. You just have to make sure it’s flashed well before you cut. I always fill with soapy water and let stand a few days, drain and repeat, drain and I go to work on it. I have never had any safety issues at all. When I am done and ready for the burn out, I get it as hot as I can, then it ready to sand blast and paint.
Good luck and have fun.