I can't give an authoratative answer (for RAM usage) for the standard PICBasic Compiler (PBC) as I don't use it, but the Pro is constrained only by the limits of the PIC you are using. I have applications with hundreds of variables working just fine. For PBC consult the product specifications, or even send MeLabs an email directly.

As tenaja suggested, use an array. I use just this method for taking multiple sequential ADC readings, and I'm sure you will find suitable examples posted on the forum. The ADC on a 40MHz PIC is fast enough to capture Audio (not exactly Hi-Fi but it does work) - but you have to send it to external Memory as the internal EEPROM is way too slow.