Look around for a cardboard box to mock it up, or set up something over some chair backs so you can test the height you're contemplating. If it's too low, adjust your base to raise it up, if it's too high, adjust to drop it down.
It IS kind of sucky that they charge for their plans, but you've also got to realize that this is their business. There's a reason you have to pay for toilet paper....it's the manufacturer's business....either way, you aren't FORCED to pay....you've done QUITE an admirable job drawing up your own plans...I won't comment on not buying toilet paper LOL