Well, the gun "safe", or in this case, metal cabinet is the best idea. By the way, mine is 55" tall - I edited my 1st post after I realized I had left that out. It's really a small footprint and is easily concealable if you don't want casual visitors to know it's there.
As far as cases, get at least one hard case, and one soft case. You are much more likely to damage firearms in transit than in the field. Don't carry a gun in your vehicle without a case if you don't want to see it damaged. I use a soft case for local hunting/range trips where the gun just sits by itself in the backseat and a hard case for longer travel where it might be riding with camping equipment, etc. Hard cases are usually lockable, nice when I visit my friend in south GA who has kids. You can pay what you want for either style, soft cases start about $9.99 and go up to $1000.00 plus for custom leather. Hard cases go from about $15.00 to whatever you wish to spend. I tend to stay on the cheap side, plastic cases are fine for me. If you plan to travel by air with your guns or go on safari, you'll need something different.
Be careful when buying cases, shotguns are typically several inches longer than rifles and won't fit in rifle cases or will fit poorly. Double gun cases are nice, but be sure that the two guns fit without touching each other or the sides of the case itself, otherwise you will see damage on the parts that are touching.
I wouldn't so much buy a book for maintenance instruction as I would just look up the individual firearm on the manufacturer's website, they will also send you a free manual if you ask. The advantage here is usually you will see a schematic diagram and get specific instruction for that firearm. You mentioned only shotguns, so you'll be most likely getting 12ga, 16ga, 20ga, 28ga or .410ga unless you are getting something really exciting. The easiest thing to do would be just to buy a generic "gun cleaning" kit. It will have everything you need and will do the job. However, I would encourage you wait until you know the gages you are getting and do this:
1.} Buy a one piece cleaning rod, made for shotguns. They are much thicker than rifle one piece rods, and don't flex, bend, break at joints, etc. (Use a cheap cleaning kit a few times and you'll see what I mean. There are times to save money, but don't do it here). You don't need one made of carbon fiber or compressed moon dust, but get a one piece cleaning rod.
2.} Buy bore mops (looks like a tiny mop), brass bristle brushes (you won't use these much), and a slotted tip. The mops and brushes are gage specific, but the slotted tip will work with them all. The slotted tip is, well, a piece of plastic or metal with a slot in it to hold patches. Some folks use a "jag" which is a pointy metal or plastic tip that holds the cleaning patch, I like the slotted tips. Either way, go with plastic tips, you are much less likely to damage a gun that way. Also pick up some cleaning patches, the girls don't like it when you start cutting up sheets for some reason. These are also available by gage. You can cut your own from old t-shirts and sheets, but just buy them. You'll be happier.
3.} Buy a cleaner/lube/protector. There are hundreds to choose from, do your research on the web, opinions differ, but I like Break-Free CLP™ and old fashioned Hoppes #9™. Your guns were most likely cared for with Hoppes #9™. CLP™ is a modern cleaner/lube/protectant, and Hoppes #9™ is a bore cleaner, but it has lubed and protected many generations of guns. The advantage of CLP™ is it doesn't harden like regular oils after time. Avoid or at least do your research on cleaners that claim to clean with no work on your part or dissolve everything in your barrel. These can be harmful if not used properly. Especially with older guns and Hoppes #9™, you will see a clean bore one day, followed by some fouling it has brought out of tiny stress cracks in the metal the next. If it's been a long time since these guns were well-cleaned, you will need to look at them every other day or so for about a week.
4.} Follow manufacturer's cleaning instructions. Clean only from the breech (where the shell goes in) to the muzzle (where the shot goes out) if possible. Less is more with gun oil, don't soak a gun in oil, you'll only attract dirt and cause jams.
5.} With older guns like these, I would strip them as far as possible and clean them up. Years of old gun oil and lube are waiting to cause slow actions, ammunition feed problems, or a whole host of things. Most guns can be cleaned without disassembly, but you are asking for problems with older guns if you don't throughly clean them. If you aren't real handy following directions and tools, leave this to someone else. If you do decide to take them down, be sure you use the right size screwdrivers (very important) and have a schematic on hand. Take all wood or plastic parts off and spray with non-chlorinated brake cleaner and scrub with an old toothbrush. Watch for spring loaded parts, they can fly off into nowhere fast.
Another thing with older guns, be sure they are safe to shoot with modern loads. Late 1800's to 1930's production guns can be unsafe with modern shotgun shells, if you have some older guns, be aware of this fact. Also, shotgun shells are made in 2¾", 3", and 3½", be sure you are buying the right size, guns chambered for the longer rounds will function with the shorter, but not vice versa. If these guns are of recent manufacture they probably will have screw in choke tubes to accommodate various hunting/shooting situations. You'll need a choke wrench to remove and install the chokes and somewhere to keep the choke tubes (hollow steel cylinder, usually 2"-4" long)
Feel free to ask any other questions, and be sure to validate my advice with your own research.
