@type is either individual or organization, and organizationType gives more precision about the type of organization, e.g., non-profit association or cooperative or company, etc.
size of the logo should be reasonable, that is, something like a PNG or SVG that goes into a 512x512 square/circle for example. Again, it’s best to have a look at what others are providing. See especially groups: they range from 96x96 to 480x480. Try finding the best size to quality to filesize ratio.
tagLine is the (one-line) motto of your organization (e.g., Best hoster in town), while description offers a longer form (e.g., We’re a friendly cooperative based in our hacklab in Utopia offering free and paying services.)
As a rule of thumb, have a look at other librehost.json and start from there.
This is not the case, we do have some individuals. One of the interests is to be able to share knowledge and time together. Once you’re not a lone fighter anymore, your system becomes much more reliable by addressing the bus factor.