Where in the original post did the OP suggest aerobatics? I agree that aeros is the best sort of flying you can do when you just want to have fun, but AFAICS the OP is more after high-performance (turbine?) singles and twins. (As if it's more fun to burn fuel at 300 knots than at 100...)
Does anyone have an opinion about how likely it would be to get low cost hours as a SIC in Southern California with pilots who have single pilot or multi crew ratings and need a SIC pilot for ratings / insurance reasons, ICAO fights to Canada / Mexico, ferry flights etc?
I think you need a bit of background on how a pilots license works. Note that the details vary by country, but in general your license consists of a number of parts:
1. The "license" itself, which defines the pilots privileges with regards to renumeration. PPL, CPL and ATPL are the most important ones here, but there are sub-ICAO variations as well (NPPL, LAPL, RPL, they come under different names).
PPL -> May not act as a member of the flight crew on a revenue generating flight; has to cost share or pay 100% of the direct costs of the flight
CPL -> May fly for renumeration
ATPL -> May act as PIC on a scheduled airline flight
(That's the very short version - read your local Air Law books for details)
2. The medical. Not exactly relevant in this context.
3. One or more "class" or "type" ratings. Class ratings are typically SEP (for single engine piston) or MEP (for multi engine piston). Some countries also have a SET (single engine turbine) or MET (multi engine turbine) rating. Above that, a rating is type specific. (And for seaplanes you'd need an additional rating/endorsement as well.)
4. Your license may or may not include an Instrument Rating, which gives you the ability to fly outside VMC limits.
These bits are not totally independent. For instance an ATPL requires an IR, a class 1 medical and a type rating on a multi-engine, multi-crew aircraft. Plus a certain number of hours in such an aircraft.
In your case, what you are looking for is a SIC role in a type-rated aircraft such as the Citation on just a PPL. That's going to be very interesting. There are a few pilots (John Travolta and his 707 SIC rating come to mind) that do that, but it does take serious money. Why?
- If the aircraft is not a multi-crew aircraft but can be flown single pilot, there is no SIC role as such. I'm not sure if you can log the hours if you pretend to be SIC under the FAA system, but under JAA, if it's not a multi-crew aircraft (by the POH/AFM/CofA or by the SOP of the operator), you can't. You're effectively a passenger. (Although it's a lot more interesting than being a passenger on a commercial airliner.)
- If the aircraft is a multi-crew aircraft both pilots need to be adequately licensed. Not just for the aircraft, but for the type of operation as well. So if it's a revenue-generating flight both pilots need to have a CPL at least. Plus of course the relevant type rating.
So the only time you'll be able to log any hours on a mere PPL, in the type of aircraft that you aspire to, is on non-revenue generating flights. (And if the ferry pilot is being paid, it's already a revenue-generating flight, I think.) So essentially this only works if you can pay for the flight completely yourself. That takes John Travolta kind of money.
Another issue is insurance. Even if you were to get your own 707 (like John Travolta) and have a PPL with the right type rating, insurance may require additional things. John Travolta's 707 type rating is limited to SIC only, for instance: He has to hire a fully licensed ATPL with 707 type rating to fly the aircraft as PIC.
The good news is: A CPL isn't all that hard to get, and gets rid of a lot of limitations. On the other hand, type rating exams are typically at the ATPL level, so it'll be extremely hard to get a type rating without an IR, for starters.
Oh, and the definition of "aerial work" within an aviation context is different from "work" as on your visa. It may well be (but you'd have to consult a visa expert for that) that your visa allows you to occasionally act as PIC/SIC on a flight and perform aerial work (assuming you have a CPL) for which you're not being paid.
Aerobatics doesn't seem too bad now, does it? Just a PPL/SEP with possibly a tailwheel endorsement required.