Upload & Sell: Off
Note that the idea of using Lr is that you don't need a search engine because the files are indexed and the Lr catalog knows where they are already.
My keyword index has evolved a bit on the fly but not too much. My best tips are
1. give it a bit of thought up front without over-doing it
2. start simple and add complexity only if required.
3. Until the retrieval takes too much time you don't need to add more categories
4. Don't forget about collections. Sometimes they are more appropriate than keywords, or else they may just help you grab the photos that will be assigned a keyword.
5. Keywords can be multiple words but I tend to link them with an underscore because that helps me distinguish whole keywords from partial keywords where the same word is used in multiple keyword categories.
6. Always add new sub-categories before unassigning a master category so that the images do not disappear from view when they have been selected by master category. Otherwise they become much more difficult to find.
For example, I have a keyword category called vehicles. Eventually I broke that into cars, aircraft, boats, etc. If I had lots of aircraft photos then I might add helicopter, planes, etc. under aircraft, but not until it became too hard to find the helicopters amongst the planes. Under cars I gradually added my cars, my brother's cars, etc. but only because I started taking lots of photos of maintenance procedures and they were obscuring the general nature of the cars category.
Do it in such a way that master categories do not need to be removed - spelling changes are easy in Lr, but structural changes are harder to implement - but add sub-categories. Anything in a subcategory will appear when you search for a master category, as will anything that is tagged with the master category but not one of the sub-categories.
Give it a go because it becomes clearer with usage. Use your own categories because they will be what matters most to you.
Avoid categorising with metadata that already exists, such as lens model, unless you are tagging film scans for which you happen to know which lens was used. There's no need to double up and make work for yourself. However, you might want to make a category for shots that were taken with less than the 1/FL shutter speed so that you can more readily assess your hand-held shooting capability in terms of image sharpness.