1 Any opinions or recommendations on what I should look out for on this?
2 Will the 5.4 turn a 305 tire with out to much stress?
3 Will the awning rattle itself off and land in a cactus on a Baja 2 track?
4 Will the existing tranny (e40d?)hold up with the bigger tires?
1 Nope, looks good.
2 Yes, Chris is doing a lot of 5.4s these days. It will get the job done, but maybe not as briskly as a V10 or diesel. Don't expect better fuel mileage because it will be working harder to get the job done but it will do the job fine. I expect you'll average about 12-13 mpg with bigger tires on that rig. Call Chris if you haven't. He's very helpful and can tell you a lot more about what he can do to suit your needs.
3 No, it should be fine. Lots of hardcore SMBers have awnings that hold up just fine.
4 Yes, as long as it's in good shape. The e40d is the same tranny used in most ford trucks with bigger engines and more weight than this. The 460s and 7.3 diesels all had the e40d. I would service it when you get the van. It's about time and probably hasn't been done.
Good luck, nice van!