Conference first or paper first? I am currently figuring out what would be better to do: would it be better to select one or multiple conferences first and then write for these conferences (if their topics match your topic(s) of interest)? Or would it be better to write and once completed writing, see which conferences do match your paper? What would you do? What would be your advice?
Thanks in advance!
What field? What's typical in your area? Ask your advisor.
When I was a student, in my area, computational fluid dynamics using the finite element method, things tended to go:

talk or poster (with no paper/abstract only minisymposium)
journal paper or invited paper to conference proceedings

unless it had been a while since we'd been to a relevant conference, and then we'd take a recent paper and make a talk or poster out of it to give at an upcoming conference with some added results if we had them or could make them in time. But, that may have just been my advisor's preferred manor of working. Doing that, we wrote a few papers and did a lots of talks and posters in the time I was in my PhD program. Sometimes we'd do a paper for a conference that required a full paper (e.g., the AIAA annual meeting) and have to wait much longer on acceptance than something that was reviewed only on abstracts or extended abstracts.