That would depend on your eye sight. You typically line up with a shiny pencil mark. If you stop mid stream you have a kerf to line up with. Not saying it would be hard but time consuming to get it perfect and you won't know if it is perfect until after you make the cut. My expectations are for better than a TS cut yours may not be.
For the Festool and the most secure, 2 bars, $15 each.
Well if as you say fairly straight is all you are looking for you might be happy but as I have mentioned before I am looking for better than TS results. Moving the track at all upsets the accuracy. Not moving the track at all will give you the straightest line.
Remember these saws are not framing/construction saws, they are made to produce very very straight and good cuts.