A cavaquinho is four steel strings on a short scale and a small body, played with a pick and rarely allowed to stop moving. Almost every gear question it raises is really about tension on a small top — what it can carry, what it does under a hard stroke, and what happens when you ask for more than it has.
These are explainers, not a catalog. No prices, no brands, no reviews: this site has not handled the instrument you are about to buy and will not imply that it has. What it can do is tell you what to look at, in what order, and what each thing changes about a figure at tempo.
Where to start
If you do not own one, start with your first cavaquinho. If yours has started sounding tired, read strings first — steel on this instrument dies quietly and gradually. If it sounds fine and fights you, setup is the page.