Focus on sorting out one thing at a time well, because the "wants" and costs are never going to end
8" is a lot more light sucking power than the 6" - you may regret not getting the 8" later on.
If you get hooked you'll eventually be buying more cameras, guide scopes, guide cameras, computers, laptops, software, possibly an off-axis guider, focus motor, dew heaters. It all starts with the mount and OTA.
8" on HEQ5Pro is a very workable combo. I've only ever used F5, but believe F4 a lot more demanding to collimate and focus for the extra FOV you gain. Guiding around 1000mm focal length is a reasonable challenge best of times whichever you buy. Just be aware you're getting in the deeper end of the pool if you skip starting with out with a refractor.
What camera will you be using?