1) yes, that's a monthly cost for 1 year. at about 1 year into your subscription, you can cancel or renew (for a higher cost, i believe).
2) yes, that's an annual (1 time) payment. at about 1 year into your subscription, you can cancel or renew (for a higher cost, i believe). note, the monthly payment and lump sum payment should total about the same amount you owe adobe so i'm not sure about the amounts you posted. in usa dollars, the monthly is ~$10/mo payment and the annual payment is ~$120/year.
3) at about the 1 year into your subscription (after 1 year you have a 1 to 2 week grace period when there's no penalty for canceling), you would cancel your photography plan and subscribe to a single app plan (for lightroom, if that's the app you want to continue using).
4) you can add apps any time. you're never blocked. in your example, you would have two subscriptions with different expiration dates. note, having 3 (or more) single app subscriptions makes no financial sense because it's less expensive to have the all apps plan (but adobe allows it, i believe).