1) If you get a weight distribution hitch, then you *ought* to be able to level the vehicle without modifying the suspension o the Sequoia. As far as recommendations go, there are several active threads right now, where you can see a variety of opinions. Just do a search for "recommended weight distribution," and you should see several hits.
2) If you are worried about the jack post, pull it up to its highest position, then get an electric bandsaw and saw it off to where you think it should be. Now you will need to se it on a block or wheel to make up the difference, but at least you won't have to worry about clearance. But, I would wait to do this until you decide what weight distribution hitch you want. They tend to hang down well below the A-frame, and you might realize that your jack post height is not going to be a problem after all.
3) Get a weight distribution hitch with sway control built in. I have an Equilizer, which limits sway in 4 dimensions. I quite like it--others will have different recommendations.
But all of the above recommendations are going to be dependent on your eventual loaded tongue weight and cargo weight. If you are going to leave it gutted, then you can run out and buy a hitch right away. If you are going to build it out, and add granite countertops, you should probably wait to buy a hitch until you know what your loaded trailer actually weighs.