Hi there
Fuel if stored correctly will last for years. Methanol is hygroscopic ( absorbs water from the atmosphere ) so the container must be airtight. Nitro ( if added ) should be kept in the dark. The container must resist being attacked by the fuel. You should also keep it away from children's reach and/or in a childproof container and if in any quantity outside your house ( here in NZ more than 5 ltrs of flammable liquid stored inside your home will void your house insurance). I mix my own fuel in 20 ltr batches and have had no issues ( apart from running out!! ) As for running the tt15 / .40 trainer etc I strongly suggest you join your local club as there will be someone who can show you how to set up the engine an how to ( hopefully ) adjust the carb to get it to run correctly. All the new members to our club get to use the club trainer ( aircraft ) and are supplied fuel, I am sure this will be the case at your local club.
Best regards Steve