Hey Stiffy, welcome to the DCS World of adventures!
Unfortunately I never had X45, so I would not be much of help, but I had a X52 and still have X52 pro. I guess they must have something in common. So, I assume X45 has a three modes same as X52. Your goal is to set as much as possible on the stick and throttle, so you don't have to let them go without a good reason. I used to program three different modes, one for combat, one for flight controls, one for everything else which does not fit in to the two previous categories.
Some controls will be present in all modes, for example air brake, you need to have it in the same place in all three modes.
Take your time, profile is individual thing, it will take time to realize what you want and where. Some things you will understand while flying... "ah, I need that thing on the stick, here should be nice place for it...". So, take it easy, it will come :)
Once again, welcome to the DCS Club!