The only way to really find out how much abuse anything will take is to go just beyond that level and break something. THEN you know where the line is... just behind you. /forums/images/graemlins/crazy.gif
If you're planning on mowing something like you described I'm not sure a finish mower is what you need. That's why there are rotary cutters out there. A finish mower is for mowing lawn-like areas, not areas with bricks, 3" branches, etc.
As to rollers, they are to help you eliminate scalping your lawn when the middle area of your mower would go over a slightly raised area.
Good luck with whatever you decide to do. I hope this helps. /forums/images/graemlins/smile.gif