One part of the question is simple, the other is actually quite complex.
First the simple bit - the filter. Filters are easy enough to do on the browse, use a conditional filter. Use a session variable, set (presumably) by a form field on the calling form. (set session value using simple "send new value to server".)
Now your "jump into lookup near closest record" gets a tad complicated. Because in the form field you're allowing them to type either the code, or the first part of the description. If I type 11 should I jump into the lookup near code "110" or near description "11 East Boulevard"?
One approach is to test it first to see if it is a complete, valid, code. If it is jump there, if not jump to the nearest "description". I haven't worked out the kinks in this approach yet though.
Aside: Incidentally in 4.29 I've added a field to the lookup so that you can specify the sort oder for the lookup procedure.
cheers
Bruce