The R8 has that very useful feature that I keep banging on about - the ability to go into Record by pushing a footswitch. This means you can drop in something extra on an existing track, or make a correction, while your left head is ready on the guitar neck and your right is holding the plectrum.
You mention about looking at the next model up. That's a good thought, because only being able to record two tracks simultaniously is very limiting. Supposing you wanted to record yourself singing and playing rhythm guitar while backed with a stereo drum unit? For that you'll need to record four tracks simultaniously. Then you want add an extra lead guitar track and maybe a tambourine . . . . . you';ll be needing extra playback tracks too. Paying a bit more for extra simultanious recording tracks and extra playback tracks can be a good investment.
I use the Zoom MRS-1608, an older model with 8 track simultanious recording and 16 tracks of playback and even then I'm quite often running out of tracks, as I did when recording the music for The Triumphs new Youtube video,
Meeksville (Down The Holloway Road)http://www.youtube.com/watch?v=MYR2HhBWsCkAs well as vocals (double-tracked), k/b, guitar, bass and drums(several tracks needed for drums), the mix includes things like handclaps, fingersnaps and three saxes (alto, C tenor and Bb tenor). The tracks just filled up and I had to borrow an extra one from the Piccadilly Line at the beginning (joke)
Ray