RE: Is 16.8V for the starter safe?
Not only is it safe it will be the best starter you ever used. I built the first one four years ago and it has seen near daily service since. Used an el cheapo hobbico starter and two 3000 Nimh seven cells in series. Have built two more for team mates since. It does have a downside and that is the tendency for it to keep disappearing from the my pit and the need to go down the line looking for it.