I tend to agree with stkjock. God that's painful to say. Anyways, I actually love the concept of compound turbos, ask just about any Supra owner and they'll jump right on the band wagon. In the world of drag racing, I think a compound setup is an absolute waste of money and effort on a gas powered modern Ford motor. If you were doing a diesel swap, I'd say get 'er done. So far, you've been talking about modular 3v max effort setups. But hey, it's your money and effort and we'll certainly tag along for the ride.
To your question, will the small turbo create a bottleneck. The answer is no. All of your piping post-low pressure turbo (the smaller turbo) has to be conducive to the high-pressure turbo (larger turbo). However, it's up to you to do the math on turbo sizing, CFM, and how much PSI is behind that CFM being pushed into the intake manifold. If you size your turbos poorly, you'll have a low-pressure turbo spinning its guts out and a high pressure turbo playing catch up, defeating the purpose of a compound turbo setup. You only need 1 WG for the low pressure turbo, which should be located between the combined exhaust source and the LP-Turbo. This WG will act as a bypass to the HP-Turbo. Once the smaller turbo is spooled to the desired PSI, that WG will go wide open and bypass the exhaust to the HP-turbo, and continue to freight train the larger turbo. That's all that 1 WG needs to do. Not sure where you think you need a 2nd WG on the LP-Turbo. But again, there shouldn't be a bottleneck unless you're beyond its efficiency range, and if your LP-WG has the correct spring pressure, the LP-Turbo should never spin beyond its max efficiency. If you size both turbos correctly, account for all the different pipe sizes, length of pipe routing, it should spool as designed. There are plenty of smaller turbos that can push 30-40 psi efficiently.