Congrats on getting started! I hope that you will only need to apply once! I have experience applying to 2 schools both through OTCAS. Hopefully my answers to your questions will be helpful for you!
1.) The NEW OTCAS cycle will open around July 2017. DO NOT fill anything out right now or create an account. Everything will be gone once the NEW cycle hits. I HIGHLY recommend making your account and start filling in the info in July.
2.) I did my personal statement while in the process of completing my OTCAS app. I highly suggest making the OTCAS personal statement very broad (i.e. talk about why you want to become an OT/future goals you have in mind) and NOT make it school specific. For example, say you talked about USC and how you want to go there for their amazing faculty in your personal statement and uploaded it into the OTCAS personal statement section. EVERY school you submit an OTCAS app to will see this essay! You will see when you start selecting your specific schools you are applying to that they will ask for "supplement material" such as another personal statement, additional questions, etc. USC, for example, does not read the OTCAS personal statement and instead ask for a supplemental essay which has a very specific prompt. It really depends on the school you are applying to. I would research EACH school to see if they require a supplemental essay.
3.) Depending on the school you will apply to, most schools allow hours to be in progress. However, there are some schools that require 40-80 hrs to be done minimum before applying. Again, I would check specifically with the schools you are applying to. In addition, you CANNOT add additional hours to your OTCAS app once you have submitted an application. The way you "submit hours" is by submitting a time-sheet or any document that contains your hrs that is signed off by your supervising OT.
Basically, OT schools are not very uniformed in their deadlines so all schools have different deadlines. Once you submit one app to one school, you CANNOT make any further changes to the application as a whole, UNLESS it is a pre-req that is in "progress". But OTCAS will only allow 2x a year to make changes to your OTCAS app, which is usually when the school semester is over. (hopefully this makes sense) OTCAS gives ALOT of warnings regarding NO CHANGES can be made once you submit an application.
4.) Additional tips--- Like I said previously, OT schools ALL very in terms of deadlines, the type of admission, and pre-reqs. It makes it very difficult for us because their is no sense of uniformity. If you research that a school has "rolling" admissions, it is BEST to submit your application as early as humanly possible. For example, I know SJSU has rolling admissions, and the earliest you can submit your application is October 1st. Schools with rolling admission basically admit students in a "rolling" basis meaning they can get full even before their deadline, which why it is important to submit your application as early as possible. Other schools such as USC, have a hard deadline and do not do "rolling" admissions. They simply review all the applications at the same time a few weeks after the deadline.
Some other tips I have is to do your research thoroughly! You are applying to a lot of schools! OTCAS is really tricky to use, but their customer service is really helpful. Just read the FAQ in the OTCAS website and it will surely help you for this upcoming application season. Luckily, I didn't have any problems regarding OTCAS, so I am sure it will be fine as long as you read the directions carefully.
Hope this helps!