I don't know.
many Access project start like yours but then the business outgrows it, but then by the time you realize that you are then stuck with Access and have nowhere to go as it is doing all of your business logic and has turned into a monster.
we originally moved everything to PHP and MYSQL, but have since converted most things to Java and MSSQL, with a little bit of C# here or there.
Our path probably isn't too helpful to you. i work for a university primarily developing internal applications. The majority of our decisions on what platforms to use are made based on what our slave labor (students workers) are capable of doing, so this is probably not necessarily what would work best for most businesses. The students may be cheap but they have extremely high turnover, as we can't keep them after they graduate. To be fair we do pay them and this is one of the highest paid student jobs available on campus. we have a short time to train them and get them productive before they leave, we have to work around their class schedules during the school year so we only get them part time, and considering they are still taking their CS classes they often know little to nothing when we get them. considering those limitations, i think we do quite well and the students that work for us get some valuable work experience that has helped them start their career after graduation.