You can set the number of lines in the Embedded View properties on the form to, I think, 3000 lines. Or, if you used $$ViewTemplate for MyView, the reverse is true: you can call the URL to open the view w a count:
Regarding substitutes for @Command([NavigatePrev]) etc : Just use that on your form, and then look at the source. You will see that it references a UNID for the next or previous in a list of docs. In this case it sounds like the restricted category is foiling the expected list of UNIDs, so you could build a view that delivers all the UNIDs that a particular category would yield. Put the list into a computed for display field, and referernce that. That should take care of it.