I would say that the first thing to do is to decide on a track plan. The type of benchwork will in large part be determined by the plan. Get some squared paper, and draw about 40 or 50 plans that will fit your space. Will your road be point to point, two levels, around the walls, or what? Once you have a plan, you can draw it out on large sheets of paper (full size) on the floor of your space to make sure that everything will fit. Then you could submit the plan to the trackplanning section of The Gauge for comment and suggestions. There is a lot of experience and expertise here. You will get some good ideas. Once you have done all this you will be ready to start serious construction and then we can start to consider open grid, L girder, cooky-cutter or whatever. There is a great temptation to rush into your first project but rushing rarely results in getting the best you can in the space you have!! Don't ask me how I know this.
Post some plans.
Have fun.
Ralph