+1 ... this is exactly what I do every year.
To sim a "Coach Dynasty" I consider myself a young upcoming coordinator getting my first shot as a head coach. In an attempt to keep it "realistic" I ONLY take over a team that would potentially hire a first-time head coach in the real world, so this usually means a 1* or 2** team. My favorite years are usually between year 2-4 as the team is molded into my own play style and progressively improves (i hope). I always stay at my first head coach position for a minimum of 2 years, and usually 3-4. Once I have achieved some consistent success I then consider myself ready to take on a position with a struggling BSC school, or build up a mid-major (ala Boise St).
For example the past two seasons I would have loved to eventually take a position with a team like Michigan, Tennessee, or even Florida St (if they have dropped from top 25 in game). Traditional powers that had fallen on hard times with consecutive bad seasons. Or take over a BCS school that never has quite achieved great or consistent success. Schools like Michigan St, Iowa St, Minnesota, etc). For the mid-major route there are numerous options ... the last time I took over Ohio U and built them up until I got an invite to the Big Ten. I figured that was a perfect fit with Ohio St as a natural rival. If I remember right I replaced Northwestern which seemed like the logical team to take out at the time. Only thing that sucked about that is their stadium is very small and EA gives us NO option to create or build a new stadium which would obviously be required if a mid-major did make a conference jump like that?
The one thing I've never done is immediately take over a top 25 school. It's just too easy to recruit with those programs, and they're already loaded with above-average talent so achieving consistent success is too easy which makes for a boring dynasty (imo).
Gotta be creative and use your imagination to keep the game fresh!