We had a wonderful time staying in Lisbon during Web Summit. The apartment is in a super central yet quiet neighborhood, great to get anywhere, however do plan for cobble stones and bring flat footwear. It's hard for Uber / taxis to come into the castle area, so I wouldn't recommend coming with a big suitcase (or be prepared to walk 10min up hill).
The apartment has everything you'd need - and there's plenty of cafes and restaurants for any price category within 15min walking distance so you wouldn't want to cook anyway. Do get supplies in the supermarket on the way from the metro station, the nearby mini market has a lot but is not open late.
We'd definitely stay here again, with this location it's really living like the locals.