i registered in mid-january and got everything set up and ready by the end of jan. I took the mcat mid-may, and took a month off around feb because of crazy personal life. That being said, I set steady pace and still didn't finish everything. I left off studying verbal, because that was my strongest section, and focused on bio (because I hate orgo, but wanted to rule the bio section) and physics (because I was strong in gen chem already). So having about 4 months worked for me, along with taking 15 credit hours and working 25 hours per week.
Try the AAMC 3R online (it's FREE!!!) and use it as a diagnostic. I scored 6 points higher on my real mcat, after studying for 4 months. I only practiced with AAMC tests, but that was due more to time constraints. I tried to take a practice exam every 2-3 weeks in the beginning, and then every week the 2 months before the exam, and then the week before the test I took 2 more. I had the last week before the exam completely free to study.
The topical tests are helpful, if only to show you exactly WHERE you are struggling, and because they help familiarize you with the format of questions. Everything (all the tests) were online. I'm not sure what you're asking about tutors, but if you want a tutor, they cost extra (a LOT). for physics, do the NOVA book. It's under $30 on amazon and it will rock your world.
Frankly, the lessons aren't insanely helpful content wise. They teach what concepts are heavy on the test, and their strategies to tackle those concepts, but you don't learn content from them, it's more like review after you've read the books and done the preview homework.
in terms of expiration date, join NNNNNNOW!!!!! mine was supposed to expire right after my exam, but magically extended itself an extra 4 months anyway. And you can always call and tell them you've decided to take it in april, and will they extend it for you (they're usually super nice about this).
so, only you can really know if you have the time and discipline and energy to study in that short a span of time. The good thing is that you can always bow out of the january test in favor of april's and then you've got those extra months if you need them. I felt rushed always, and i basically abandoned my friends for awhile, but they were nice about it. and i still wished that i had 2 extra solid weeks of studying right before the exam, but it would probably have been overkill. this was a crazy long post, so pm me if you have more questions.

