Buying MVC points

I purchased 2K points for my family of 7 four years ago and have used the heck out of it. Between the points, earned bonvoy points, interval certificates we have been on 16 trips for 82 nights. I'm one of the few people who seem to enjoy the points and want more. The only regret is I purchased retail and didn't know about resale. So I have a few questions I haven't been able to find the current answer to in the forums.

1) The fees Marriott charges for buying resale seem to have evolved quite a bit over the years. To my understanding the current fees are about $3/point on top of my resale purchase. Is that correct and are there any other fees I should be aware of? 2) There are a lot of Jan use year for sale. I read a lot of those are converted weeks and when you purchase you get the original week and not the points. Is this true or outdated information? If true how can you tell if you're buying points vs a week? 3) I currently own a Sep use year (we travel off season, beauty of homeschooling). If I were to buy a different month can I combine them into the same use year or am I stuck juggling different use years? 4) How long is the process of buying resale? 5) Are there any drawbacks of buying used MVC points like there is with Disney?