My first question is "How is the business doing after 11 years and where is it headed in terms of current growth, customers, founder(s) vision etc". If the answ

My first question is "How is the business doing after 11 years and where is it headed in terms of current growth, customers, founder(s) vision etc". If the answer is negative, then the technical improvements won't matter much. But let's say that the business itself is doing good and there truly is a need to improve the tech now to help do even better. In that case, DO NOT DO A FULL RE-WRITE. DO NOT. sorry for caps but it is important. Like many others have already suggested, start with a smaller piece and improve it. May be create a separate API/service. Then measure the improvement in developer time and customer happiness linked to it. Build that slowly over time. "I want to keep things simple, and avoid bringing in too many dependencies, so I am leaning towards a minimal set of Symfony components, rather than something like Laravel" That is good thinking. "One of the primary complaints we get is that our current system is too slow. In part, this is because most actions trigger a full page reload." Instead of a full rewrite, focus on improving te performance here. Yes, a full rewrite sounds exciting but how will that impact the business ? Instead, what if you figured out a way to improve the current performance bottleneck first ? Remember that customer don't care about tech. They care about a solution that solvs their problems fast, efficiently at a reasonable price. I am also concerned about the fact that a junior dev is being asked to rewrite. I understand it is just 4 of you but depending on the number of customers you serve, do not take this lightly. Source: I have built software and run my own SAAS. 20+ years of experience breaking shit in production.