From a performance (UPS) standpoint, are chest transfers or belts best? I'm thinking chest transfers since you can set it to only update once every couple of seconds (which as long as you can't fill an entire steel chest in that time is usually sufficient), but I don't see anywhere in the FAQ where this is stated. Guessing the same is true for the fluid transfer pipes vs regular pipes?

Yes, chest connections are much better for your UPS than belt connections. A blue belt connection has to update once every 3 ticks to ensure compressed throughput, a chest connection can wait up to 600 ticks. This means there's much less Lua code to run, which is always good for performance.

By the same principle, transfer pipes are much better than regular pipes to connect with, since they too require much fewer updates for the same throughput.