Laptop and eGPU with or without iGPU


I am about to buy a laptop with Thunderbolt 3 with the idea of connecting full-size card via razer core.

I have two questions I cannot find a meaningful answer for.

1.) Would I benefit from purchasing a laptop that also has an integrated RTX card? Would I have to switch between them (rendering the integrated card useless) or can they both work in a meaningful way on the same training set?

2.) Because Thunderbolt3 has a max theoretical throughput of 40Gb/s would it be an overkill/bottleneck to use RTX Titan? (This is not for gaming.)

Thank You.