It's possible to gather all the info you need for the FAFSA in december, and all you need for taxes except a few forms like a W-2, but still know exactly what will be on the form. Waiting until Feb is unnecessary, and can make you less likely to get grant money if they pool is limited. You don't have to sumbit your income taxes to fill out the FAFSA, only complete and sign them. I submitted the FAFSA in Jan last year, but sent in my taxes (which were completed in Jan) later, because I didn't want to send the IRS any money before I had to.
If you have more schools to apply to than the amount of spaces on the FAFSA, you fill it out with the first six (is it nine this year? It was six last year.) Then after you get confirmation, you "correct" your FAFSA, by changing the schools to the next bunch of nine, and if you are like I was, you wait for confirmation and correct it again.
If you file online, it takes only a day or two to get confirmation and then change the schools. If you read the instructions, this is what they tell you to do, and they don't actually remove the schools you initially listed. So all the schools will get your info.
As to deadlines, it depends on the school. Some give out money as they get applications, and may run out of the best funding if you are later than other applicants, even if you are technically "on-time." Other schools have deep pockets, and won't run out.