Access has one of the best report writers in the business. Not only is it highly capable in its own right, but it's fully programmable with VBA.
In my younger days, I designed and built Access applications for law firms. I also gave several presentations at local Bar Association events. (In the early days of personal computing, lawyers at the biggest firms were expected to design and build their own litigation support databases.)
I've had 80 concurrent users, and quarter-second response time on normal queries with 2 million rows. But designing Access apps to do that isn't trivial. For a few concurrent users, you don't need to do anything exotic. Number of rows doesn't matter much. (Much.)
Still, I think your best first step is to build an Access app with two files: one for the tables and their relationships, and another for everything else--forms, reports, links to the other file, and so on. That way, should SQL Server become necessary, you can just migrate the tables to SQL Server and relink them in Access.