Sounds like a plan Ron! As for the baffles height, that will depend on a few things...
(1) Will your skimmer opperate at any water level? If not, you will have to elevate the skimmer somehow to enable it to function properly or set the water level low enough so it will function properly without being propped up.
(2) How much "space" will you need for back siphon when the return pump shuts off? That will be a pretty hard one to just estimate, but depending on how you set it up, it won't be a major issue. Here's an example...When I used the sea-swirl on my return pump, I forgot to drill a hole in the nozzle to break the siphon when I turned off the return pump and when I tested it, the water almost came over the top of my sump and I had to plug it right back in so it wouldn't flood. I ended up putting a bunch of holes in that thing (even started a thread to get help) and in the end, the back siphon was still so much, I had to expand my sump so that I could have a little more "play". You can use check valves to prevent back flow, but in any case, you still don't want to set the thing too high just incase they fail. So that has to be taken into consideration.
(3) Is salt creep going to be an issue? Yes if the baffles are too high without a lid on the sump and if you use a lid, you have to worry about heat. So something to think about.
So those are some things you can think about first to help give you an idea on how high you need to set your baffles. Everyone is going to have their own opinion on a height, but ultimately it will be your set up so you will have to make them to suit your needs best. Just on my opinion, I like baffles (if being used like a bubble trap with 3 of them stacked side by side) I like them 1 inch apart and a 1 inch gap at the bottom for the water passage way. I can get a pic if you need to show you what I mean. As for total height, did you decide on if you were using the 55 gal for sure yet? Let me know and I'll think about it a bit