I have described a bouncing laser mirror system for accelerating space vehicles to very fast speed. How would braking work ?
The braking is done with a receiving laser bounce system at your destination (like Mars)
you would need to carry a good superconducting magnetic sail to slow you down
I would say that you first send over the robotic parts and gear on slower trips. Bigger, slower payloads with aerobraking and whatever else you have for braking. Maybe an early package would be the nuclear gas reactors (still to be made but on the drawing board) and laser, mirror systems. Send those multi-ton packages over on 96 day or 6 month trips. Whatever speed that you can brake safely from. Then the receiving lasers have power. Then you can do a better job of slowing in bound shipments. Then you can start sending things over faster. Go twice as slow send 4 times as much stuff. Go ten times slower and send 100 times as much stuff. The laser/mirror system is still very efficient in terms of the cost of consumables (mainly just electricity).
Ultimately a network of laser systems for accelerating and slowing vehicles would be needed.