I find a good mobile app is very useful to store information about your Bonsai collection or for making notes and reminders for the jobs that need to be done. You can store a lot of information per tree, such as purchase date, purchase price, measures, purchase source etc.. I use Bonsai Album by Andrew Nicolle. I think it's only compatible with iPhone. But there are certainly similar apps for Android. It gives you statistics and synchronises jobs that need to be done with your agenda. Very handy when you have several trees.
Bonsai trees aren't cheap. That's because a lot of effort and time has been put into making them what they are. At specialised shows you will have a great possibility to compare prices in relation to the quality of the tree. I find a Bonsai tree to be a good investment as long as you are sure of taking care of it. The older it gets the more it's worth. When you buy a Bonsai tree make sure you know the latin name and check its health and eventual parasites or diseases.
Books and videos
There are very good books about the art of bonsai on the market. Sometimes it is more accessible to watch a movie about how to prune or repot a tree. There are quite a lot of informative videos available on Youtube about keeping Bonsai.
The best thing of course, is to join a bonsai club where you can exchange information and ideas with other members and where courses are given at the same time. This is where you will learn the most and realise that not only you make mistakes.
Protecting your Bonsai
Excessive exposure to sunlight can damage your trees. In the summer of 2020 it nearly ruined my collection. Especially the pine trees were badly affected and started to become brown and losing needles. Some might say that Japanese Pines need full sun exposure. I'm not so sure of this. They will survive in nature in full earth but in a pot is a different story. In very hot periods I now protect them from UV rays with a protecting sunshade and move some of them in a shady place. Also watering at least twice a day in such warm periods is recommended.