If you are looking for strong, long lasting, high quality work that looks professionally done, then nails are not the solution I'd ever choose for joinery of this sort.
Nails work well between a pair of 2x4s when you are framing a wall, but that is where I stop using them. If you are expecting finishing nails to hold any serious load, don't. That does not say that finishing nails have no purpose. They can work nicely to hold together a joint while the glue dries - no clamps need apply! But even so, butt joints with glue (and a few light nails) are simply not very strong. It won't hold up over a few years. (Yes, I'll admit that I have never UNDER-engineered my work.)
So, the next step up might be rabbet joints, glued and nailed. Again, with nails or not, they simply won't offer strong, long lasting joints. In the right place, a rabbet can be the right joint.
Dado joints (a groove that fully encases the matching wood) will be strong, and will support a serious amount of weight. These offer a good solution, IF you have the tools to cut one, so either a router or a dado blade for a table saw. But a dado joint is not always an option.
Butt joints with dowels can work, but it will be somewhat slow to do. You need to be accurate in lining up the holes, so a good jig will be important, and know how to use it.
Personally, I like biscuit joinery. It helps to have a biscuit joiner to cut the slots, but a router could do the job in a pinch. It is strong, works well enough with plywood, easy enough to do. Biscuits will be far easier to use and install compared to dowels, because they allow for a bit of slop in the slots.
The last option I'll throw out is pocket screw joinery. It creates quite a strong joint, even with plywood. They are easy to line up, since you drill the holes with the wood mated together. The screws draw the mating pieces together tightly, resulting in a good looking joint. You can build very high quality case work with these joints, however, you generally want to be careful to keep the screw heads hidden. The cost is not too high for a screw jig, and then all it takes is an electric drill.
Either of these latter two options would be my preference. They will be significantly faster to do than dowels, but dowels (if done well) can offer a strong, serviceable joint.
The point of all this is it depends on how strong, how professional a job you want to do here. Are you willing to invest a few dollars into a piece of equipment (i.e., dowel jig, biscuit joiner, pocket screw jig?)
Some of those minimum clearances are defined in building codes and will vary from place to place. In Ohio we use the International Plumbing Code (IPC) and it does define some of these minimums and local municipalities might add additional regulations. But it sounds like you may not be as concerned with the minimum specifications, what you really want to know is what "feels comfortable" and looks/feels good. Unfortunately a question like that is tough to answer.
Luckily people have been dealing with small bathrooms for ages so there are a number of strategies you can employ and there are some specialty fixtures that can help, like narrower bathtubs (28” instead of the standard 30”), shallower vanities/sinks, shallower toilets (10” rough-in instead of the standard 12”), etc.
If you can find a copy of the codes your area uses that can be a good resources if you have the patience to read it. I would recommend an electronic version so you can search for terms.
In the IPC the relevant sections I found are here:
Section 417.4 Shower compartments
All shower compartments shall have a minimum of 900 square inches of
interior cross-sectional area. Shower compartments shall not be less
than 30 inches in minimum dimension measured from the finished
interior dimension of the compartment, exclusive of fixture valves,
showerheads, soap dishes, and.safety grab bars or rails.
417.4.2 Access. The shower compartment access and egress opening shall have a minimum clear and unobstructed finished width of 22 inches.
Section 405.3 Setting
405.3.1 Water closets, urinals, lavatories and bidets. A water closet, urinal, lavatory or bidet shall not be set closer than 15 inches from
its center to any side wall, partition, vanity or other obstruction,
or closer than 30 inches center-to-center between adjacent
fixtures. There shall be at least a 21-inch clearance in front of the
water closet, urinal, lavatory or bidet to any wall, fixture or door.
Water closet compartments shall not be less than 30 inches wide and 60
inches deep.
Best Answer
My interior decorator recommended about 1 meter. Also, a good tip is to put newspaper on the floor where you're thinking to put your furniture to get a better visual effect. Get the newspaper on the floor in the right position and then measure.