You can set up your own kingdom's laws, and most lords who can't produce a son are willing to name a daughter their heir, but in most cases if there is any male of age even remotely related to the family, even husbands, they will be preferred as heirs by other lords, especially to the throne of Overlord. Women are also not allowed to hold Clergy land.

More on them in the rules, but the Clergy basically possess the kingdom's electable titles. It goes Bishop [Landholder of a fief in the Clergy's name], Cardinal [Same as a Bishop, but can have a vote in the Clergy Council], and the Archbishop [The leader, who possesses the three Archbishop's fiefs]. 

If an unmarried man of noble birth joined the clergy at a relatively young age, he will likely ascend through the ranks and become a bishop, beholden only to the Archbishop, and the Archbishop to the Overlord himself.

It can be very useful to get one's sons into the Clergy, that they might take advantage of additional lands and influence.

From a roleplay standpoint, women rulers will also be looked down on by their subjects, until they can prove themselves to be competent, and thus worthy of serving.

Oh, and before I forget: pillaging!

You can raid trade routes, farmland, towns, and manors for plunder.

Trade routes are convenient routes followed by caravans that travel between towns. They are the fastest ways between the towns, and so almost all merchants looking to make their fortune will use them. But even a heavily guarded caravan will likely be no match for a Lord's retinue.

A trade route will always exist between the two towns. How much can be plundered from a caravan is based on the wealth of the two towns the route travels between. To get a trade route's wealth, you simply take the two town's wealth level and average it, with Wretched having a value of 1, Poor 2, and so on.

So, all the possible trade routes are:

1 + 1 / 2 = 1

1 + 2 / 2 = 1.5

2 + 2 / 2 = 2

2 + 3 / 2 = 2.5

3 + 3 / 2 = 3

3 + 4 / 2 = 3.5

4 + 4 / 2 = 4

4 + 5 / 2 = 4.5

5 + 5 /2 = 5

The amount of loot you get from a trade route, based on its value:

1 = 5,000

1.5 = 7,500

2 = 11,250

2.5 = 16,875

3.0 = 25,312

3.5 = 37,968

4.0 = 56,953

4.5 = 85,429

5.0 = 128,144

A trade route can only be raided by anyone once per season, including NPCs. If a trade route is raided for four consecutive seasons, then the wealth level of both towns the trade route connects goes down by 1. If both towns already have a wealth value of 1 (both are Wretched), then trade stops entirely for the rest of the year, and all through the next (if those four seasons ended with the Harvest season, the last season of the year, then trade simply stops for all of the next year), which is simply due to the merchants of either town going broke, or abandoning any hope of making wealth.

Raiding a trade route takes seven days.

Pillaging farmland will simply give you 1 bulli for every 2 people, rounded down, regardless of its fertility. It will take three days to pillage a fief. A random number of people will be killed in the process, and the people will not be able to pay taxes to their liege that annum. If you wish, you may spend extra time pillaging the infrastructure and resources. Each will take two days, four for both, but will yield you with half the bullis or/and crops that will be produced in an annum. Doing this will cause the level of either to drop by one level. A fief can only be pillaged once per annum.

Pillaging a manor will yield the fief's stockpile: all the crops in the kingdom's current stockpile, divided by its number of fiefs, and rounded down. It will also yield 1000, 1500, 2250, or 3375 bullis, based on its respective level of manor (Wooden, Fortified, Stone, Great). Pillaging a manor will take 12 hours.

Just realized I need to work on the rules for pillaging towns, so I'll get back to you chaps on that.