I switched to fullalt back in August. If you really want to learn that playstyle, the sooner you begin, the better. Here's what i did:
0. (Very strongly recommended) Say goodbye to singletapping for a very long time. Just don't do it. You need to relearn taiko from zero. Reinforcing your singletapping habits will make the process harder.
1. (Optional, but recommended) Create at least three playlists. One for kantans. One for futsuus. One for muzus.
2. Go here.->
http://osusearch.com/ Get beatmaps between 150 and 260 bpm. The more, the better. At the very least get one for every 10 bpm jump. I'd recommend a minimum of two.
3. Begin with low bpm kantan and climb your way up. I was satisfied when I was able to get S or A ranks with very few misses on each map. Feel free to play maps from the next difficulty level when your'e past the 200-220 bpm threshold, but make sure to not abandon your current difficulty until you can confortably play at 250 bpm or faster. Repeat until you're back on muzu.
4. As it has been said before, the jump to oni will be very challenging. But for you
it's all about learning the patterns.
By the time you're playing high bpm muzus and trying to get used to oni level it becomes less about the bpm and more about the patterns. Dont feel ashamed to try out stuff in HT.
5. At first you will only be able to play the most basic (very low bpm, around 3*) onis. The climb from 3* to 4* is about rising up the bpm while getting used to the longer patterns. You may be stuck there in a while, but don't get too frustrated. Try older maps with mods when overwhelmed/ play stuff for fun, like songs you really really like. You won't need a "guide" to rely on from that point onwards. Keep challenging yourself by stepping slightly outside your comfort zone every once in a while, and I guarantee you, you'll learn the game. Best of luck.