You shouldn't re-do any level. You earn less points and you might use a power twice and lose it (I don't think it's stated by the game though, which is weird). Just start the next one you haven't completed yet, you'll have many digs and good points.
And you should put all your points in joint strike (25% less armies required is insane), alloy sell value and money/resource caches boost.
To have more chances to find good artifacts concentrate on 8H digs, more artifacts/day. Or the cheapest if short on money. When you'll have the artifacts you desire it won't matter anymore as they all statistically take the same amount of time to reach an insane artifact.
Keep the inspire mercenaries to have a x5 for the later levels, it allows to complete them easily Basically you should always finish a level with 5 powers everywhere (excepted multi-levels as they are the hardest to get).
One trick for flash start the levels is to use all the starting money to boost the first army camp then use supercharge army camp then x5 free cache. With this you easily reach the first market, even the second + a few hospitals on the way).
And you shouldn't hesitate to do the hardened levels. They may take more time but they give much more points and the bonuses are great. The amount of points alone makes the hardened levels interesting. Some people avoid them, it's a mistake. With markets/alloy sell value/mercenaries I find them easier to complete than normal levels as they have many powers (easy to double time warp hospital upgrades to move on).
Here is a link that helps to do levels, if you want:
https://pkmx.github.io/wzi-levels/europe-huge.html
Edited 8/27/2023 13:02:37