OK Neil, seeing as you asked:
1)...if you have the Stew Mac routing template - chuck it in the bin. I don't know who came up with that but chances are they had modifying a standard Strat in mind, it's fiddly, confusing, not very well thought out and urges you to take more wood out than you need to.
2)...buy a Kahler if you play like a pansy. If you're used to a Floyd a Kahler gives the same feel as deleted by mod
OK, from the image you posted it would sort of work but i'd not make the ledge quite as wide as you can get the base plate hitting it before the fine tuners are at their full depth so it'll try to pull the base plate away from the studs. You can champher this transition to help ease the situation or as i said earlier, just start the deeper route a little closer to the studs but leave around 1/8" between the edge of the stud and the new depth.
As for having the whole route at the same depth - not the best idea and will depend on exactly how deep you need to be. Having the studs half way up their travel isn't ideal as you've indicated.
The main thing you need to consider depth wise is the height your neck sits from the body, obviously if you have the chance to reduce the heel depth then you have the chance to reduce the depth of your floyd route.
If you have anything specific send me a PM on the UKGB forum as i rarely log into the mail address that PG is connected to.