Hello!
There is no option of splitting those 12 subjects into chunks - one has to sit the whole lot of them in one go.
Not any more since a couple of years. You can go as often as you need as long as you stay within the timeframe of two years. But they charge you the full examination fee every time you go. Be advised that some employers want to have a look at your training records and taking too long (and/or too many attempts) for the exams will not be your best recommendation.
The schools are under extreme beaurocratic pressure from the same authority...
Not more than in other countries (in my previous company we operated Italian owned aircraft under our German AOC because the owners wanted to avoid Italian bureaucracy...). I go to a training organisation in the UK every year for my sim refresher and compared to what they have to endure from the British CAA our LBA is easy-going!
...and the price for every bit of activity from that authority appears to be extortionate.
Really not more expensive than in other large western european contries. And as before, rather cheap compared to the CAA.