You are right to try and get the discone up as high as possible.
Not only will it improve signal levels from distant sites, but it will reduce the amount of noise/interference from electrical appliances in your home (particularly on VHF and AM Air bands).
Just make sure you use good, low loss coax. LMR400 is an excellent choice..
Wind loading of the mast and to a lesser extent, the antenna, will be your biggest challenge.
Can you use three equidistant guy wires on your mast, 3ft or so beneath the discone?
That will stop the whole thing falling over in the first strong wind.
What can go wrong, will go wrong!
FuncubeDongle Pro+ - PSR600 - PSR500 - BCD996XT - BCD396XT - TM9155 - IC-208H, amongst others :-)