As Sir William has said, start with what you know and work back towards what you do not know - yet. It is far easier to find parents of grandparents of someone than the other way around.
If you tried to work forward from Alexanders profile you would immediately be having problems as the profile shows no children or sources.
By adding your branch to wilkitree, with all the information you can find and list the sources of the information you will quite quickly get back a hundred years or more, and you may find cousins who are researching the same idea. You can then collaborate and build on your joint histories.