You'll need to learn alot more before learning how long it takes to dry the leaves. It's not the leaves you'll be drying for harvest, it's the BUDS

Read, Read, Read. After you're done reading, Read some more.

To give you a general answer. You should plant about double the amount of seeds that you want plants. It is common that half of them will turn out males. My first grow, I planted 10 seeds and 5 were females. You want to grow females so you get buds instead of seeds. I would recommend a 400W light to grow some decent plants. But alot depends on your particular grow room. I will also say you need about 4-8 weeks to veg and then 8-10 weeks to flower depending on which plant. Then you can dry for 1 week and cure for 4 weeks, more even better. You will learn that you don't have to wait all this time, but if you do, you will getter better results. You will have to learn the enviroment of your attic. How hot and cold it is when your light will be on and off. There is so much to learn that you will have to READ, READ, READ. Hope this helps.