1. I learned the hard way that a good practice when one does prototyping (or first revisions) is to leave some breakout regions in the board; in case an extra component or a connector needs to be included, there is room for it; otherwise, one may end up with kludges like the one in the photo below.
2. Spacers, those expensive small plastic cillinders, with a screw through them, used for tightening 2 boards together: make them from discarded pens, just cut to the desired length. I used them in my Wide Clock.
3. Battery holders can be attached to the case with velcro. One can use velcro even for boards.
4. Push buttons that look similar may be oppositely different, that is, one closes the circuit, the other opens it. The latter is sometimes called "touch button". So, be careful and make sure you use the one you intend to.
(to be continued)