[Fantomen]

There is no "norm" regarding either the size of expansion parties or overtaxing, you have to ask nation specific advice.

Many nation guides gives an more or less specified idea of how to expand with that nation. The actual method might be any of the following: good quality troops and good scales (sometimes combined with overtaxing), it may be sacreds, it may be a national summon (MA agartha), it may be an awake pretender, it may be some elite special unit, it may be elephants. Or something else. And so on.

Most of the time, pretender build plays a role in the expansion. Either by providing the scales or a bless or expanding itself.

Good expansion can also be achieved with "normal" scales and troops if you script cleverly and pick targets carefully. This is the hardest path to learn, but it has the advantage of freeing up design points for mid and late game priorities. My recommendation if you strive to learn this is to begin with a scales build and good troops, like a MA pythium scales build, and then shift down to a harder choice (like Man with neutral scales) when it starts feeling easy. When you can consistently win against a given poptype with a specific tactic, start to reduce the number of units you send to find the sweet spot where you can expand with as small parties as possible. Because the smaller you can make your expansion parties the faster you can expand, remember that you can always have two expansion parties teaming up for a tough indie.

The point is that you need to find the specific expansion strat for the nation you're playing. As for cash, obviously you cannot afford everything always, and there is a random element too. But the general gold supply is evidently enough to establish the standard I have proposed, since it is the expected performance in most MP games and has been for years.

The reason to strive for the suggested minimum of 12+ provs and 1 extra castle, in standard settings, isn't that it is some magical number or anything, but simply because that is what you can expect other players to achieve. And naturally you will be in a subpar position if you cannot match that. It's not required to always achieve that or even desirable for some strategies, but it is a good baseline to practice for.

But basically, you are asking a specific question without providing the specific details needed to answer, of which the first and most basic is what nation you want to play. It is possible to detail turn for turn how expansion and gold expenses looks like, but only on a per nation basis.