I do not think there is a rule of thumb answer to your question. And setup questions for TT and pursuit for USAC / UCI are different than triathlon.
To give you an idea of how ridiculous UCI rules are, you and I would essentially ride the same bike with maybe a slightly different setup such as seat height and aerobar pad spacing.
The gating question is do you want to be UCI compliant for pursuit and TT? In general, USAC seems to becoming more lax in enforcing rules even at national championships but they are sticklers when it comes to setting record.
My wife and I train and race in UCI compliant setup. This is the way we started and now we can do it so why change what works.
If you ride UCI, then the limits are 75 cm from the centerline of the crank to the end of the aerobar extension and the nose of the saddle must be 5 cm set back from the centerline of the crank. You can have one morphological exemption. 80 cm for the extension or zero offset for the seat setback. I take the 80 cm and ride on the nose of the saddle.
The other limit is the tilt of the aerobars and the tip of the bars cannot be higher than 10 cm above the pads. This is somewhat of a must have when buying aerobars. Some racers are slower in the raised bars position but most are not.
Moving the pads fore and aft is a matter of stem length and generally one does not want ones knees to hit the pads but you can see that it starts where you plan to put your ass. So if you deep six UCI, you could slam the seat more forward then you need a longer stem and aerobars.
I have a bag of stems of different lengths. Do not buy any stems. I will give you the bag and let you play around with them. Then you can figure out which one works and take that one or buy one.
If you want to get masked up and come over, I will show you our setups and once you see how to do it, it is trivial to set up a bike. It is less trivial to optimize for CdA but that is another matter.