Use GFILL. Then when you lose health, decrement an amount from the length of GFILL. Since health will likely be 100 though and your GFILL coordinates will likely be entirely different, you should be able to figure out the math for that I'll let you figure that part out.
I have a feeling they will still release it on Wii U. Who knows I guess it's mostly up to smileBOOM. I doubt it could really gain much (performance wise from the Switch) mainly because the Wii U already has enough power for SB. Also the U price will likely drop and increase the player-base rather than decrease.
Basic is a high level language (very human readable), it's pretty easy to learn. Certainly easier than both C# and Java. No one can give you a time frame but yourself. 1 month of hard work and you could learn a lot though.