Everything below is said with the advantage of 20/20 hindsight regarding what worked in "Enterprise" and what didn't. I'm sure that if I hadn't seen "Enterprise", my prequel would be completely different.
Thing is, I don't think "Enterprise" was so bad in basic concept. Setting the first season in 2151 was a good decision because you don't want the Earth-Romulan War to completely overwhelm the series, but you still want to include it in the later seasons. I don't mind at all that we've never seen a Denobulan before -- we never see a 24th-century Andorian or Tellarite either. The ship design doesn't bother me either -- so it looks like the Akira-class, so what? How long was the Akira-class actually on screen, about twelve seconds?
The problem with Enterprise was the execution. Season 4 goes a long way to rectify the problems, but it's obvious that they were simply fixing the mistakes. The growing alliances between the future founding members of the Federation, the reformation of Vulcan society, the growing Earth fleet of Warp 5 ships, the growing Romulan threat -- that's all stuff that should've been building up from day one. Then the Romulan War begins at the end of the fifth season.
(Now, you may be thinking "But if the show lasts seven seasons, then it'll be due to finish right in the middle of the war! There'll still be two or three years left over!" But I have a solution: in the series finale, the ship gets destroyed in battle. Then the crew all get reassigned to different ships, and a follow-up movie/duology/trilogy/television-miniseries follows all
those ships for the rest of the war rather than just one ship at a time.)
The approach "Enterprise" took to the technology and look of the show was the right one: it was much more sensible to project 150 years in the future rather than 100 years back from Kirk. The only changes I'd make there would be changing "phase pistols" and "phase cannons" to "lasers", and "photonic torpedoes" to just "torpedoes".
Regarding the Daedalus-class ships: technically, that ball-and-three-cylinders design was never actually identified as the Daedalus-class on screen, so I'll say that was an older class of ship and make the Daedalus-class a more advanced-looking design with a saucer section rather than a sphere.
Oh, and one more thing: I wouldn't call it the Enterprise. You know what's a good name? The Hyperion. Not only does it fit mythologically speaking, but it also sounds space-y. I think it's the Y and the fact it ends with "-ION".