1. more than one; 2. just one; 3. if together, then just one; if separate, then 20; 4. maybe 20 individual ones or maybe 10 sets or maybe less. It depends on the grouping. That is, how many people per reservation?; 5. 'drizzle' is a noun. 6. 'a light' follows the same structure as 'a little'; 7. There will be...tomorrow. Either a drizzle or drizzles; 9. & 10. Try, there will be (a) light rain tomorrow.