This may or may not help your decision making. There are 2 different question threads this should be broken into:
- 15" i7 or i9 model which offers the 555x and 560x
- 15" i9 model with the 560, Vega16, Vega20
If you're thinking the i7, I'd do just the baseline items ($2,400). If you're going to do any upgrading, do the second one, with the i9 as it's base cpu. It'll have the 560x, plus the 512gb ssd & the i9 for $400 more (but would cost $600 to add to i7 base model). Since they all can do eGPU's, doing the Vega's seems to be unnecessary unless you're a road warrior who's editing footage on a plane.
The one other thing I'd consider is how long you tend to keep a computer. Personally I'm at 1.5 years on my 15" 2017 MBP, and did over 6 years with the previous one (2011 with dedicated graphics, see earlier thread). If you keep a machine longer, or it's your one and only workstation, I might lean to the $2,800 model. Otherwise the $2,400 (possibly with a larger ssd) would be my recommendation. Just keep in mind that the 13" they sell only offers the Intel integrated option