I too really hesitated when we had only Wylie, and then started thinking about getting another...it felt like such a big decision and I became very indecisive as a result. I finally bit the bullet and went forward and I am SO happy I did, bc that brought our little Marcel into our life, and he was meant to be ours.
Although I now have 4 dogs, I do think 2 is the ideal number bc it's still easy to travel with 2 etcetera.
If you get another one...Chester may be insecure/needy for a while, but he will get past this, I promise.