You have a lot of relevant flight experience, but you will need the commercial obviously. Also, for smaller operators, assume that you will need a CFI also.
You'll need to get a commercial SE & ME, and a CFI, then acquire 100 hours multi. You could either buy 100, or get an MEI and teach. Buying it would probably be cheaper and easier for you.
At this point you have two options....
If your local field has a thriving corporate/135 community and you know or can meet someone, you might be able to get a part-time jet or prop job in the right seat. It's all about networking...if you don't know anyone, it will be tough.
Or, you could get a job at a regional airline (preferably flying the CRJ), get 1000 hours jet (1.5 - 2 years), and then start applying for corporate jobs. The 1000 hours jet time is key, and the CRJ is VERY similar to the Challenger biz jet. This would require a sabatical from your IT job if that can be arranged.
I'd get the commercials, CFI and MEI, and the 100 ME...by the time you have done that you should have a feel for the situation in your area.
Note: the fractionals tend to work 7 on, 7 off, so that would not really be part time...you're probably looking for a local 135 or private operator that wants to have a pilot (maybe a backup pilot) on call, but doesn't want to pay a huge salary. Actually I have friends who make $60K+ to be on call for private operators, and they only fly 2-3 times per month.
You'll probably want a first class medical; while technically not required, many professional pilots who have a second class have some medical problem that precludes the first class...you may not want an employer assuming incorrectly that you have medical issues.