I think it's fine. Having the other ideas floating around in your head can et distracting. also when you grow tiered of one you can start working on another one and you still get to work on your righting skills. Then when you get boared of that one you can go back.
It depends on how well you multitask. I get other story ideas when I am working on a story. I make sure I write them down so I don't forget them and then save them for later.