Just to put this is more direct english, since it sounds like you’re just getting started:
The slower your engrave speed, the wider your engravable area will be. That is, slower speeds will give you larger area to work with.
The higher your LPI, the more passes it has to make, and the longer the job will take.
Of course, slow high-LPI engrave plus full bed = LONG jobs, well over 3 hours.
If maximum size is your goal, just be prepared to compromise on LPI and/or sit and watch it for a very long time.
As for cutting out the border, again, it sounds like you’re just beginning, so I would suggest reading some of the getting started materials, you probably have about 100 questions you don’t even know to ask yet, this will really help you get going:
I know that reading a forum for hours isn’t as exciting as lasering some stuff, but it will absolutely pay off. Get a drink and a snack, kick back and study up! Enjoy 