I've been using WA Extensions for a number of years. As a rule of thumb I suggest you take a look at the notes in your download centre for each extension you plan to use for your project. Quite often there are notes posted there that will help you out. For example, some extensions needs to be installed before others in order to avoid conflicts in the future, or some extensions may need to have a patch applied if you're using certain other extensions - an example of this is Form Builder 2 and HTML Editor 3 (Form builder has a patch that needs to be installed before HTML editor 3 in order to make the two compatible).
Also, these support forums are a great resource when you need help. The advanced search functionality allows you to search for specific answers about specific issues - I visit the forums regularly and have found answers to all of my problems here, either from others users, or from WA tech support staff like Jason and Ray. Learn to love the forums, they will be invaluable to you.
Hope my advice helps you out.