Have Dell XPS 13 and need to add external graphics card and GPU, will this one do?

Well, which exact model of the XPS13? And how old is it? (I am asking because the XPS 13 line has had many generations, going all the way back to the 2nd-Generation Intel Core CPU days of early 2012.)

The problem with that particular GT 730 is that is almost completely useless for GPU acceleration in Premiere Pro. In fact, it is actually slower than today's integrated in-CPU Intel UHD or Iris Graphics. You see, that GPU uses extremely lousy DDR3 VRAM that has a maximum memory throughput of only 14 GB/s. That's far slower than even main system RAM!

And with this severe mismatch in the memory throughput between the CPU and the GPU, the CPU will end up being bottlenecked by the underperformance GPU. This means that overall performance in Premiere Pro when not using the GPU (that is, in software-only mode or when CPU-only effects or no effects whatsoever are used) would actually be significantly slower with that GT 730 than it would with just the integrated Intel GPU.

In addition to that, the GT 730 is much older than most of the CPU platforms that underpin the XPS 13: That particular GT 730 is actually based on the over-seven-year-old second-gen Kepler architecture using the GK208 chip with only 384 CUDA cores. Nvidia driver support for that GPU is now on the brink of being EOSL'd (End Of Support Life'd). Plus, CUDA support had already been depreciated for all Nvidia GPUs that are older than the GeForce 900 series in the newer drivers beginning with the release of CUDA 10.2 (which debuted with the 440.xx-series display drivers).

Hence, any discrete GPU that's weaker than integrated graphics is IMHO not worth paying even one single cent for. In other words, avoid all GPUs that are almost obsolete for Premiere Pro (as that GT 730 is about to become obsolete very shortly).

By the way, that is not an external GPU card at all. It is actually a slot-based internal graphics card that's meant to be installed internally inside a desktop PC. As such, that card by itself will not work externally at all with any laptop. You will need an external GPU enclosure with a Thunderbolt connector if you are going to use an internal desktop GPU externally no matter what. And that is where I have determined that such a low-end and outdated GPU is unsuitable for this use.

Lastly, only very recent models of the XPS 13 have Thunderbolt capability at all. Most older models do not have Thunderbolt at all. Therefore, your particular XPS 13 might not accept external GPUs at all.