#1 you dont NEED expo to fly 3d its very convinent but i know a guy who learned with no expo and still insists on it that way, i love it personally but you dont absoutely NEED it.
#2 3d planes or aerobatic planes toned down auctually really arent that bad, if thats all ya got why wait to save up for a trainer grab someone who knows how to fly and you can probably learn on it.
#3 if you can get the cub go for it i know that a lot of people have started out there and are still going, it definately gets you into it right!