And no, I don't think the UFP should expand.
People should be free to expand as they see fit as long as they don't do it in a way that causes unnecessary conflict.
The Universe is VAST, there's plenty of room to expand.
They should be concentrating on improving the lives of the people within the federation.
That's everybody's job, it's not just the government, everybody should be helping on improving the quality of life of everybody else.
They should be building large space structures like Yorktown and Dyson spheres,
YorkTown just seems so ostentatious, I'd rather go for various size Ring Worlds.
Dyson Sphere's are too resource intensive, and the crew of the Enterprise-D found a existing Dyson Sphere that is built, just TerraForm the surface of it and adopt it / use it.
Turn it into the Noah's Ark / UN of the Federation.
Also adjust the Star so that it's more stable, there are plenty of Star mining techniques that they can do to make it a more Stable Star.
enjoy life and building up their defensive capabilities so Earth doesn't have a single ship in drydock every time a whale probe, Nero, or V'ger comes knocking.
I concur, the UFP is woefully under defended, especially given how many planets it has, how many citizens there are of the UFP.
In time perhaps go entirely virtual, building a series of interconnected holographic universes within their own aegis so that economies of scale can have the Federation developing the equivalent of millenia while outside barbarian nations continue to slowly blood along. And just genocide the Borg before they get the same idea.
Why? The existing Borg should get dismantled and any form of "Cybernetic Hive Mind" should be eradicated & blocked.
If resources are plentiful and there is more than enough room for people to live, then what is driving all these people to start new colonies? In this post scarcity society, why are there still people mining limited resources?
All resources are finite, you can convert one element to another, but that usually consumes energy to do so.
Sometimes you can gain energy like in fusion, but that's a different matter all together.