I suspect in an ideal world, they'd like 150-200km events; but can't afford to run events of that length. Thinking back to when the BRC was last in a golden era, the F2 years, these were the events:

March; Vauxhall Rally of Wales - Mid/North Wales. No longer runs
April; Pirelli International Rally - Kielder Forest. Now run as the Kielder Forest Rally, BTRDA, but outside the BRC. 1 day/ 45 miles.
June; RSAC Scottish Rally - Southern Scottish stages. No longer a BRC event, still counts as a SRC round. 1 day/ 45 miles.
July; Seat Jim Clark Rally - Duns. BRC, and SRC.
July; Stena Line Ulster Rally - Antrim. Returns to the BRC next year.
Sept; Manx International Rally - Isle of Man. Not run since 2017.

The Trackrod was in the BRC from 2002, and has been in, then out, and returned as a BRC round.

I think 6-7 properly promoted events is the optimum number you'd want to see. And I don't think we should have a round in Europe, despite it being a great event.