Simon, welcome to iFly. I think that what you're asking for is pretty straightforward to accomplish.
After completing your flight, look for the History tab at the bottom of the iFly screen. Pressing that will open up a menu, second item should be Show Past Flight Trail.. Selecting that will take you to a page with past flights in chronological order. Select your flight by tapping once, then look for the export button at the bottom left. That should open up a menu allowing you to share it via different means, I generally use gmail to email the link. Note that the exported data is in the .gpx format.
If you just want to see the flight path, press and hold the selected flight. To get max altitude you'll need to open the link in another program, I use Google Earth which can easily import the data. Once you've imported the data in GE, find the file (usually under Temporary Places) and right click it to the submenu that will allow you to select elevation data. The GE screen will split allowing you to trace along the flight while showing you both the terrain height and the max altitude along the path of the route.
Adding a custom waypoint while in flight can be done by pressing on your ownship icon. A set of green circles will appear first, followed by an Options menu that includes the choice to add a custom waypoint. There might be an easier way and if so, I'm sure someone else will chime in here to help out.
Hope this helps.