Tape together 2 pieces of graph paper (use 1/4" sqare rule) side by side so squares match-up at the joint. Use 3/4" to the foot scale, so each square on graph paper represents 4". Use a compass and ruler for your drawing aids. Draw the benchwork Andrew drew to scale to fit your space.
The 2006 Model Railroader Planning annual (on sale at hobby shops) had a separate section on how to draw scale track plans. I strongly suggest you buy and read it. It has instructions on how to make accurate turnout templates.
Next rough in the main line. I recommend using 22" radius, not 18" radius curves and Atlas #4 (really #4.5) turnouts.
If you prefer, you can download the free Xtrak track planning software for your computer. Or, Atlas has the free RTS planning software for download, but RTS is limited to Atlas track libraries only.
Then, when you have your first stab at a track plan done, present it on the forum here and we'll help you improve it. This is, after all, your model railroad designed by you to fit your tastes and space. We don't really have enough information to provide you with a design that will suit you. I'm not sure you really know yourself what you want - and that's OK. It's all the more reason for starting small, and then expanding as your desires are refined bv actual construction and operation. Your comments about a figure 8 with 2 duck under hatches, and about a point-to-point being OK lead in 2 very different directions. Are you really excited about doing the switching to break down and turn a train after a fairly short run - every run? There are some people that are, and that's great. There are others who need to just watch the trains roll around a loop, no matter how boring that may seem to others. How about the other operators - do they share your views on operation? Desired train length remains undefined. And you still haven't answered about passenger cars and large steam locomotives. If you intend to have either, 18" radius is too small, and even 22" is questionable. 28" radius would be about right for the passenger cars and large locomotives to look and operate reasonably well. But without passenger cars, and using smaller steam locomotives and strictly 1950 era cars and diesels, 18" is an acceptable radius.
Again, it's your railroad! Have fun with it!
my thoughts, your choices