Congratulations on your decision to go with Canon and the 400D. I'm sure you will be delighted with it, even though it can't compete with the lovely retro styling of the A-1. Here's a bit of gratuitous imagery for those who don't know the camera.
It's a shame you can't use your old lenses but, as you know, they need an adaptor and still won't focus at infinity. They might
be of use for the macro work however but you would need to do some research on that possibility. Here are a few thoughts on possible choices for new lenses but please bear in mind that I own none of the following except the 50mm f/1.8.
The EF 50mm f1.8 II is great value if you are looking for a portrait lens for the 400D but if you are into macro work then the EF-S 60mm f/2.8 USM Macro would seem to give you the best of both worlds. Would a dedicated full-frame equivalent focal length of 96mm be good enough for your macro photography?
Of course to get the equivalent of your current 50mm prime you are looking for a focal length of around 30mm on a cropped sensor. At the sort of budget you are implying Canon's offerings in this area don't receive unqualified praise but neither do the third party primes either.
As for wide-angle zooms, the Sigma AF 10-20mm f/4-5.6 EX HSM DC might be worth considering as a cheaper alternative to the Canon EF-S 10-22mm f3.5-4.5 USM. Both Tamron and Tokina offer similar models.
For a more general purpose zoom I am sure you have read and digested Gordon's EOS 400D / Rebel XTi lens upgrade group test
. Unfortunately you have to look elsewhere if you want a general purpose zoom with a dedicated macro facility and, as far as I can see, doing so means losing out on IS. The Sigma AF 17-70mm f/2.8-4.5 DC macro has been well reviewed and might be a possibility. Would you consider using Canon's EF12 II or EF25 II Extension Tubes as an alternative to a dedicated macro lens?
I'm not clear on your needs at the telephoto end of the scale. What sort of focal lengths (and budget) are you aiming for initially?