First off, battery chemistry matters. For deep cycle LA chemistries (including FLA & AGM) you have ~50% usable capacity. And cycle life will improve the less of that you use. So best case (or worst case, for your batteries), 200AH is 100AH. With Lithium, you've got ~80%.
Also, you have to consider how much you're pulling at any one time. The AH rating is usually based on a C/20 discharge rate. So for 200AH, that's 10A continuous. Any higher discharge & you're going to see less in actual capacity. Also, high discharge rates - particularly w/ LA - will lead to shorter battery life.
I'm assuming this is a solar system. If so, you'll have to consider sizing the panels so that you'll be able to restore the AH used during the course of the day. You'll also need to determine how many days of no-sun autonomy you're comfortable with. For instance, you've got one day planned for above (before considering the other factors mentioned). If it's a cloudy day, you may not get all that back. If it's a rainy day you may not get any back. So in one day, you could be done. If you're ok w/ that (generator power, etc), then no problemo. Otherwise, your AH capacity needs to double for each day you need storage for.
Finally, don't forget to add in the amount of juice your inverter is using, both in the process of inverting, as well as in standby. These numbers, particularly the former, can be considerable. Your inverter will basically be sized by your anticipated peak loads... the max amps you plan on pulling at any one time. Best bet is to try to tailor your inverter size so it meets this amount, with little excess, as the larger the inverter, the more power it draws.
EDIT. Just saw the bit about planning to use a generator. Sorry. Feel free to discount all the solar stuff then
Everything else applies however.
