[LAU] Mono tracks to mono or stereo bus ? And sampling rate

Hello all, When having multiple mono guitar tracks in Ardour and wanting to regroup them in a single bus, would that bus be preferably mono or stereo ? How is this in relation to eventually placing the guitar bus in a stereo field ? Also, is it possible in Ardour to raise the sampling rate of single tracks ? I just followed the part of the Brian Bollman music production (free) course about sampling rates. The higher the rate the more fidelity to the original signal and also the more material to work with when bringing it down to CD or ogg/mp3 level. I would like to try with the guitar and bass tracks as I don't care so much about synths for now. Is it possible to tell Ardour to work with a higher sampling rate for a track ? I don't seem to have found the option. Cheers.