Yeah, and I've taken the Practical Exam for Grade 5 (Guitar). I've been thinking of playing the cello as well, and does playing the bowed instrument interfere with my interest of playing the guitar? And one more, does my right hand's thumbnail actually hinders the bow movement if I'm playing the cello? Please enlighten me with this bass instrument.

I think it should be OK. My sister plays guitar and violin, and I don't see that cello would be so very different.

I play both guitar and cello and there should be no problem. Whether your thumb nail interferes depends on how long you keep it but in my experience a thumb nail that is long enough for guitar has no effect on bowing - the right hand side of the nail rests in the space between the frog and the binding. One advantage could be that, having played guitar, you should find vibrato fairly straightforward on the cello.