I am definitely one of the "newbies" to gardening. I'm hoping to gain much knowledge from both the veteran gardeners and the "less seasoned" gardeners as well

Today, I decided to square off a 6x6 area of land to start a vegetable garden. These are the steps I have taken thus far with starting my garden. Today, I bought some watermelon, cantaloupe, and cucumbers (they were already in the plastic containers) from Home Depot and local farmers. Then, I also purchased a pouch/pack of carrot seeds. This afternoon/evening I started taking off/skimming the grass (sorry for my lack of knowledge and not knowing the proper terminology). Now that I have the grass off...this is where most of my questions come from...so, I shall now say thank you in advance for all of the help anyone is able to share. I would like to plant the vegetables as soon as possible if it would make sense to. These are my questions:
1. Should I spray some grass killer before planting?
2. How long should I take before planting the vegetables?
3. Should I use a mixture of manure/compost with Miracle Grow gardening soil to plant the vegetables?
4. Is the 6x6 area I have designated for the vegetable garden, big enough for all of the vegetables I would like to grow?
Again, thank you to everyone! I am very eager to grow, I have a very positive attitude and I am ready to do some good gardening!!

Thank you to all!!
Rsimonew1