It will be entirely possible to get to the age of Ascension and fill out the entire tech tree before you meet anyone for war. Currently, I am on a large map with tight clusters which makes islands of planets separated by large voids. I actually like this map for this reason. It allows me to grab some planets and build a very solid infrastructure before I head off to war. 

The game I am playing I am about 280 turns in as Altarians, have 21 planets colonized with half of the entire four branches of the tech tree filled up and I just now bumped into the Earthers and Iridium. I am all set to start the war machine production now that my research and wealth planets are rolling steady with starbases helping them. 

I can easily see a very large map where you will likely fill out the tech tree or close to it before you meet another major race (depending on how many you add). 

It would make for a fun, long term campaign.