To figure out how high to make your bench you need to figure out if you are more comfertable reloading sitting or standing. Dont forget you have to make your bench strong to put up with all the force from your press(s). (dont use a hollow door)
a good thing to have by your reloading bench is a small vacum or a air compressor to remove and powder or dust. if using a progressive press dont forget to cover up the lase under the powder through die before useing a vacum or air compressor to clear any loose powder.
Another important thing you might want to consider if you have not reloaded before is a good book on how to reload. I thought modern reloading second edition by richard lee was a good one.
Have fun reloading!