SAC,
I see you started a similar thread in May of 2013, with similar type questions. While some posted about contacting Prepster or myself, I don't see that was ever done. That makes me wonder a bit?
Taking your questions in reverse, I cannot over-emphasize how competitive it can be to gain a coaching position in college. Any open position can receive hundreds of applications, sometimes more. Within that volume of candidates, along with those candidates the coaching staff might already have in mind, you have to separate yourself.
Some qualities must be included to coach, successfully in college: have a very high level of knowledge of the game and how to play it at the collegiate level, coupled with the ability to coach players and teach the game. Coaching players can mean more than what they do on the field. Since an injury impacted your playing in college, I would guess you will have to learn the college game and how to coach and teach it in a way which is pretty unique. Have you thought how you will do that?
Within this framework, I would suggest you start benchmarking against your current knowledge of the game and how it is played at the college level..
One thing you can anticipate starting out is how hard you will work and the hours you will sacrifice to prove yourself. Practice is the easy part. Early work, late work and working late into the night to be ready the next day are part of the job description.
In terms of pay, expect very little and plan on a lot of sacrifice. Volunteer assistants are usually paid something from camps. Most try and supplement that with lessons offered all days of the week. Many also try and find part time work which provides lots of flexibility, which is not easy to find.
Since you are in Texas, you might want to see if he could find a position with a HS and/or travel team for the next 2 years, where you can gain experience and actually be a coach, hopefully network some contacts, and find out if you have ability. You need something to grab the attention of coaches if/when you start sending resumes in 2-3 years. Remember, your resume will arrive with hundreds of others any time an open position is posted. Without proven experience as a coach at some level, I would expect it could be a major challenge to get past the resume competition for college positions if you have not played at the college level.
Good luck.