than gas. This means that a custom tune done specifically for your car is not nearly as important as it would be for gas. A good off the shelf E85 tune will likely do fine at your power levels. At your power levels you will probably turn off your boost controller and not limit boost anyway.
You are asking a lot of questions that have been answered many times before. This site is really easy to search and learn an awful lot of good information. Click "Pages" at the top of the page and then "Search".