Aside from the actual porting, what is required to make the most of a bridge port on an S4? Can I keep the stock ECU/FI set-up with just fuel pump and injector upgrades, or am I looking at a piggy-back/stand alone unit?

 

you would be better off with some sort of standalone, unless you could use an rteck 2.0.

turbo or n/a? what are your goals for the car?

 

Definatley N/A. I'd be happy with 200-250 crank hp.

What seals are best for a Bridge, and should I do any other internals if I plan to rev to 8k or so?

 

Full standalone, open exhaust, custom intake manifold. The stock intake manifolds are not designed to work with high overlap ports and will be a major restriction.

Any apex seal will do the job.

If you want to rev to 8K, use S5 internals including the stationary gears.