I would cut CAREFULLY up the seam of the pant leg on the cast side (just split the stitches), then roll that pant leg up and tack it neatly. If you're handy with a needle, you can do this - otherwise find a nice pretty girl to help you with it (I assume you're male). That way when the cast comes off, you can just roll it back down and sew the leg back together. Should cost a MAXIMUM of about $20 even if you have a tailor do it for you, and this way 1) you don't trash your suit, 2) still look neat and tidy and professional, and 3) you don't have to spend too much more than you already have for this process.
As for traveling, let the airlines know ahead of time. Most airlines have employees who will help you get around and get situated on the plane (and you get to board first 👍 ), help get your luggage, etc.
Good luck - crutches suck. Get a nice looking backpack or strap for your briefcase so you can cling it across your back. Just be glad you're not female. From experience I can tell you that crutches and underwire bras just don't mix.
