Wow. You raise so many questions you should probably start a new thread.
I have one of the Fighterbirds and it is more difficult to fly than some of my hotter glow fueled sport planes. That one has no elevator - only throttle and a mixed "V" tail. It borders on unmaneuverable and would be a horrible trainer.
Skis are easy to swap out. I make up a whole seperate set of landing gear with skis. As you say, around here winter is 1/2 the available season. DuBro (available at Tower) sells plastic skis for .40 & .60 sized models. Where you might get them for smaller electrice I have no clue.
Maybe the set for a Wingo from Hobby-Lobby could be adapted?
The Wingo itself is possibly a excellent choice for you as an electric trainer. It seems rugged and the one I've seen flown seems very stable and capable.
I really can't estimate the flyng characteristics of the Skyartec Cessna, even after finding their website. Looks to be a 38" wingspan on a 1-1/4 lb model. I'd say it would be a bit wind sensitive, landing gear looks light so it would need a nice gentle flair and almost no grass to preserve it and props. You're looking at a wing loading of maybe 7 or 8 oz per ft^2 of wing area. I'm used to 20 or 22 oz per ft^2; a whole different feel on the sticks. But, I freely admit almost no experience with electric motor models.
You "graduate" by becoming proficient with what you have and then starting slowly with new equipment. As always, an experienced pilot as trainer will save time and $, but if you proceed carefully you can pick it up on your own. Simulators are great as they develop your motor skills and get you used to manipulating a model coming and going from your fixed ground perspective. What they don't help with is setting up the model, balancing it properly to design center-of-gravity fore-and-aft and side-to-side, teaching mechanical techniques for motor adjustment and tuning, taxiing on "real" ground with grass and bumps and all, introducing distractions, overcoming nervousness and fear, etc. I would recommend a lot of one or two foot elevation "hops" of 25 to 50 feet length that gradually increase to longer flights. Don't try and gain altitude too rapidly (that kills REAL planes) when you make that decision to take to the air and turn her. Altitude and airspeed are your friends. I taught myself with hand-launched two channel gliders and I still was a mess when switching to motorized models. Seemed like they were either flying too fast or falling out of the sky. When I got back into this I sought out a club with instructors (and buddy-boxes) and that made all the difference.
And, from what I can tell, planes are MUCH easier to fly than helicopters and have almost no similarities except the throttle.