The width of your proposed layout is pretty narrow if you intend to have any half circles or ovals since they’ll have to have a radius less then 18″ to fit the table. I’m not sure if they still make 15″ radius sectional track but I know that 18″ sectional is available. An 18″ radius curve is fairly tight for longer equipment such as passenger cars and some long locomotives so you’ll probably be restricted in what you can operate for this reason. By using flex-track you can pretty much make any radius that suits you but, as I said earlier, the tighter the curve, the less variety in equipment length/size you’ll have.
If you intend to make a ‘point to point’ layout, the table width is less crucial but this type of layout doesn’t allow continuous operation like a circle or loop can.
I suggest purchasing or renting from the library one of the many HO layout books there out there to get an idea what you do in the space you’ve allotted. I’m sure you can find many track plans here online as well if you put something like “HO layouts” or “HO track plans” in a Google search.

Hope this helps,

Geof from the US