EC261 claim for multiple cancellations and downgrade?

The EC261 regulations seem clear enough to me when you have a single-segment journey and your flight is delayed or cancelled.

However, while returning home with British Airways going BOM->LHR->ABZ, I had 2 cancellations across 2 different days and a downgrade!

I was scheduled to fly BOM->LHR on 28-May (in Club World), and then on to ABZ later on the same day (in Club Europe). This was a World Traveller Plus booking that I'd upgraded using Avios.

The BOM->LHR flight got cancelled, and I moved to a different BA flight around 12 hours later than the original departure. The remaining segment LHR->ABZ was also cancelled.

Now, EC261 is clear to me so far: I'm due €600 in compensation.

However, when I got to LHR I received an email telling me that the new LHR-ABZ flight had also been cancelled, and I'd been moved onto a flight the next day - and that flight had been downgraded to economy instead of Club Europe!

EC261 is clear that I should be due €250 for this, but because all these flights are all on the same ticket, I'm not sure where this stands? For me, the 2nd cancellation really is yet another major PITA, and as it occurred on a different day should be counted as a separate 'instance', so I do think I should receive additional compensation for this. But that's just what I think is 'right'; I'm not sure if that's actually how it works.

Also according to EC261, either 30/50/75% of the ticket price should be refunded when you are downgraded, but it's not clear if this applies to the whole ticket, or just the affected segment. It's also not clear if this can be claimed as well as claim(s) becauses of delays/cancellations. This downgrade is an extra unnoyance to me, as it means I miss out on much needed extra legroom, can't use fast track security (I'm only in the bronze tier of BA's Executive Club this year), and can't use the lounge.

Has anyone have any experience of something similar?

Should I submit 3 separate claims, or just one that explains everything? Or am I only going to get the €600?