It’s very simple to improve your country economy,you should pay the taxes to all the services.Then try to make your surroundings to do so.Then the government will had some money for the scheme.Because the money need is essential one for the government to create good schemes to the people.
The task of the government in each country is to prosper the citizens of each country with a certain amount of money and also services that exist within the country. And it is true as you said that if every citizen is willing to pay taxes on time in everything, then welfare can certainly be realized if the government is very honest and does not complicate things that are needed by citizens.
I think you and I have a very different understanding of what governments does. I mean that is what they "should" do I will give you that, but that is not what they do at all. Almost every single government I know, just focuses on making everyone richer in their own circle, that's about it.
If you become a politician, more often than not you are already giving up so much of your integrity just to be there, not even talking about what you will do after you already became one. This is why I highly doubt that it would ever be a problem for them to need money, they will just take from the taxes. Oh new road needs to be build? Lets pay my cousin 2x what is required, and he will pay someone else to do it, and we will pocket the change. That's what a government does, unfortunately.