Cataloging..... horror, action, sci-if...etc??
Or by actors?
Have three stacks layed flat, about 10" thick each.
IMO, you've got several options. Do you want to collect, or are you looking to flip them?
If you plan to keep them, you need to first catalog them. Build a database with each poster. Title, condition, possibly actors, genre, and most important the tube or drawer it is in. Look into a flat file, or at least storage boxes. Catalog and organize. I would also photograph them. It is going to take a lot of time, but when you are done, you will have something.
If the goal is to flip them, there is a different strategy. First realize that 90% of what you have is worthless. I have looked through several lots like this one. The best stuff has invariably been grabbed by store employees and customers, leaving the stuff of lesser desirability.
Make 3 piles. One for stuff you want to keep. One for stuff you think you can sell. and a big one for kindling. Take the big pile, divide it into lots of 20 and try to sell it as bulk lots. Start bids at $1 with $15 shipping. There are additional hassles with getting proper tubes for shipping. If you don't get sturdy tubes, you will have a high rate of return of damaged posters. Major hassle. I see this as higher than desirable expenses with little return. Probably not worth your time and best to simply use them as Christmas wrapping paper.
The ones you want to keep are obvious. catalog and store properly as above. The ones you think you can sell need to be photographed and placed on eBay. Read elsewhere on selling on eBay as it has its own challenges. Since these are video releases, don't expect to get high prices. A theatrical poster may go for $100, but you will be lucky to get $10-20 for the video version. There are exceptions, but they are few and far between.
Best of luck. I hope some of this is helpful.