Your set up sounds very much like my horse tank: 46 gallon bowfront, glass top, 405 Fluval canister, skimmer. I actually find that between the flow from the canister filter and the return from the skimmer I don't need an additional powerhead in there. Experiment when you have yours up and runnig but you might find that there is too much flow with a canister filter, skimmer, and powerhead. The horses need a few "calm" places they can rest with low flow.
My glass top came in two pieces so I removed the back half where all the equipment and cords are and the front half still has the glass top. Seems to work fine for me. Im not sure about the undergravel filter - I didn't think those were recommended anymore but I'm sure you'll hear from others who know more about them than I do.
Will you be adding live rock or are you going to get all your filtration from the canister? If you're going to add rock, start looking for pieces that have "hitching posts" built in - the more, the better.
Have fun, and keep us posted!
Sue