What Grade should i be in in order to start filling out applications??

Probably the summer before your senior year. During the summer (or before) you can determine where you want to apply. Then you can look online and see if they offer a common application or if you will need to get a specific application from the college/universities where you want to apply. Then during the summer you can get a head start on filling out apps. You don't have to finish them, just get as much done as you can. Good luck!

It depends on the need. Because weather you like it or not you will soon filling up applications