Well... "seem like" and "in reality" are often two entirely different things!
That little filter is easy peasy. The translucent bowl just unscrews - there is a special tool, but you should be able to do it by hand. Try using work gloves, if needed. If you need a tool, be SUPER careful if you use slip-joint pliers - I think that bowl is crazy expensive... so maybe get the special tool. I've heard that some remove the entire assembly and put it in the freezer to help with removal? Follow the electrical wire - there is a quick disconnect further along the wire. The filter, itself, is just a friction fit piece. If your boat-mounted filter is good, and you keep your fuel quality good, you probably won't need to change the engine-mounted filter all that often. But of course, it can't hurt to do it, either.
The most important thing for the batteries is to have them fully charged. You could just remove the negative cables and let them be - they'll be fine in the spring (assuming good to start with and fully charged). A charged battery won't freeze. But removing them (or running an electrical cord) and keeping them on a smart charger all winter (not just a cheap "trickle charger", as that can still cook 'em) is the best thing you can do for batteries. I have about 8 or 10 of the Battery Minder brand smart chargers - some of them are going on nearly 15 years old, now. I like them because they also "desulphate" the batteries (sulphation is one of the main killers of batteries). I'm sure there are other good brands, too.