Harvard would open a lot more doors for you, though KU Leuven would honestly probably be just as good if not better for NT and EC. In a NT class at Harvard, you may only have a couple people who are Christians or actually studying the NT, simply because Harvard is a pluralistic place. Nasrallah is also leaving, so their NT faculty is kind of empty. All that said, Harvard is still the correct professional decision.
If you want to better position yourself for a PhD program in North America then HDS is your only option.
KU Leuven is a wonderful school with access to amazing cultural resources. There has been the occasional student here that graduated from Leuven and gone onto top programs. That said, I've also seen faculty have to google KU Leuven when someone says their name.
There is also a rather wide belief that you only go to Europe for a Masters and then to the US for PhD because you couldn't get a cheaper M* degree here. You're an international student so this won't affect you as much but being a third world applicant and getting a funded position at HDS speaks to your ability, what HDS sees in you, and what they believe that you can offer their student body.
I've never lived in Cambridge or Leuven so I can't speak to costs.
I lived on the Isle of Man for two years and as part of that process the diocese had someone sit down with me, over Skype, and do the visa paperwork. There's ways to frame resources so that you don't need to have $22,000 in a bank account but rather have access to it. I don't know if HDS has someone that can help with this but I suspect so. I know some of my international classmates at Vanderbilt from Africa and Asia did similar things too. On a US visa you'll be entitled to work up to 20 hours a week when classes are in session and 37.5 when they are not - not sure about Belgium/EU.
