An early decision is whether to employ a dedicated sustaining team versus utilizing a hybrid model where the new product development team also provides sustaining engineering fixes. Best practices for vendor usage (onsite and offsite) factor into an organizational structure decision.
Establishing a software development life cycle, SDLC, which is desirable for customers while not over-burdening the engineering team takes thought and experience. I can help you make good decisions here.
Done correctly, software branches allow code changes and bug fixes to flow efficiently between legacy and in development code bases. This protects against issues like a lost security fix. Your branching strategy needs to support your engineering team's ability to achieve the SLDC. Be proactive here.