Hi Ross, I don't think you can book and pay in advance (not ever heard that happening). They tend to release tickets approx 3-4 weeks prior to a match but that can sometimes vary. A good site to look at is the Cardiff city E ticketing site as it shows current matches on sale etc. Have you purchased a gold membership? If your doing as many matches as 11 or more, It maybe worth you doing as you get a couple £ off each home tickets, city cash (you generate cash for yourself to spend in the club shop, home tickets etc when you purchase home tickets or merchandise) - a little like a clubcard!, it also allows you to buy away match tickets. The memberships are £20 or less. I doubt you will have any problem buying tickets unless we are suddenly 1 or 2 in the league from the start of the season - most match you can even purchase on the day and we always have lots of empty seats however the price of tickets get more expensive on the day!
Basically don't worry about missing out on the tickets as you'll easily get them - perhaps ring the club shop or go down there 3-4 weeks prior to a fixture to purchase. Hope that all makes sense mate

enjoy watching the city!