Yes, Metro XL supports T9 type.
Yes, you can adjust brightness levels as per your rquirements.
Yes, you can play youtube videos on this phone.
You can store up to 1000 contacts in Metro XL. In addition, you can store up to 250 contacts in each of your sim card. So, if you are using 2 sim cards, in total you can store up to 1500 contacts.
Samsung Metro XL weighs around 105 grams.