Personally I'd recommend learning Python, rather than BASIC. You're much less likely to pick up bad habits, and it's also much easier to use once you start to do more intermediate level things. Also, Guido's tutorial (which I learnt from initially) is very good, though admittedly not the meisterwerk of John A. Coll. Support should also be better - the RISC OS port of Python is one of the more up-to-date languages ported to RISC OS so there should be no problem getting support from generic python user groups (and newsgroups, specifically).
However, if you do go the BASIC route, comp.sys.acorn.programming is probably already busy enough with relatively techie queries, but the programming forum at "that other RISC OS portal" might be a suitable place for beginner queries. I tend to check that when I'm at a loose end.