It's mostly a personal preference thing, but I think messing in single player for mods like aikido is a waste of time. Think about it for a second.
In singleplayer, you have a motionless dummy and your tori. If you practice on this dummy, you will get used to seeing the results from playing with this dummy.
The problem with that is that the dummy is motionless; only affected by an outside force. In multiplayer however, your opponents are unpredictable and always moving. This movement will affect the results and will be completely different in multiplayer.
The BEST (imo) way to get a good grip on the game and get better in multiplayer is multiplayer.
If we're talking about making replays here, then you still need to play multiplayer to learn your joints faster and better then keep playing on single player to make more replays.
Also, another great way to learn both in singleplayer and multiplayer are events. If you're doing something with pay, you're more motivated and are likely to do better. You'll also meet new people and learn from others.