The way you phrase it -- "my son's father" -- makes me think you are divorced/never married/not partnered with this person.
On a legal note, please be aware that if you hand over your son for three or four years ("in time for Kindergarten"), that your ex may have a priority claim on the child, and may win in a custody battle, if he won't return the child voluntarily. On the other hand, the life of an OTR driver is such that it might benefit the child greatly to be with his father, rather than his mother.
Also, please factor in child support in your calculations -- if he's keeping the child, legally you'd have to pay support -- of course, if your ex is so stupid that he doesn't think of getting the court to change the child support decree, that works in your favor!
I think your plan is great, and I think it's important for you to get a solid financial footing -- but please be aware that the cost may be one you are not willing to pay. I say this as a woman who -- if she had a child -- would probably HAPPILY leave it with the father and take off for the open road, as fast as she could! I realize that not all women are like me, however!
If you trust your ex to honor your agreement, I say go for it! Just realize that the law isn't going to be on your side, but on his,should he choose to change his mind.