I add almost everyone. Marriages into the tree and their parents and siblings. Sometimes more if they look interesting.
1st,2nd,3rd,4th cousins.
Cousins, their spouses, children. I sometimes take cousins spouses back a couple of generations [or more if they request it].
Back a couple of generations for non blood related aunts and uncles. It all adds up.
What is the farthest distance of a 'cousin' and how many times removed before they become so distant?. Say 6th cousin once removed, How far can you go?
Remember the further you go back with each generation the numbers of each direct ancestor doubles [2 parents, 4 grandparents, 8 great grandparents etc.]
So you can have......
2,parents
4,grandparents
8,great grandparents
16, gg gparents
32, 3x gparents
64, 4x gparents
128, 5x gparents
256, 6x gparents
512, 7x gparents
1024, 8x gparents
2048, 9x gparents
4096, 10x gparents
Then you can include all the siblings, cousins etc. in each generation.
Then you can double this if you are researching your spouse’s tree also.
I feel like I've just got started!
Tom