Much as a Character is defined by Str, Dex, Con (etc), a stronghold is defined by Economy, Loyalty and Stability. Defence and Build Points are also important.

The balance between these three Core Modifiers is important. If these three indicators are about level, your stronghold will prosper. If they get out of kilter, then bad things will happen. At low levels they should be within one point of each other, as your stronghold grows it might stretch to 5% at the very most. If the DM thinks the gap is too high, or that you are trying to work the system, he can roll on this really cool table of bad things – unfortunately it is GM only, so I can't tell you what is on there.

• Economy: This attribute measures the productivity of your stronghold or organisation and the vibrancy of its trade. This mainly represents the amount of money, labour and resources that are generated by your stronghold, although other things such as magic and knowledge are also important.
• Loyalty: Loyalty refers to the sense of goodwill among a stronghold’s people, their ability to live peaceably together even in times of crisis, and to support one another when needed.
• Stability: Stability refers to the physical and social well-being of a Stronghold, from the health and security of its citizenry to the vitality of its natural resources and its ability to maximize their use.

If you run the stronghold, you will be interested in developing both Loyalty and Stability, because most commercial empires will only be interested in Economic developments. Some organisations (Religious, Academic) are more balanced with lower economic returns but better community returns, and would be a good place to look for support.

Defence is a measure of how well your stronghold can defend itself. It is an abstract measurement of how big your army is and how well your security patrols work. A high defence gives you a better chance of spotting approaching armies, tribes of humanoids and even packs of wolves in or around your stronghold. It also indicates your military strength - the greater your defence score, the bigger the army you can raise. It is used in the mass combat rules.

At the most basic level BP are another form of in-game currency, an abstract value that represents an unspecified combination of labour, good will, magic and resources. You can only use BP for building withing the Stronghold and Investment rule sets, the two are exactly the same. One BP could include a wagon load of settlers who come to farm the land, some timber, legal services, or even spells from a caster.

You cannot cash BP in for money. However, if you do need cash you could use the BP to build (probably under the investment rules) and then sell the building for its cash value. You must get permission to build somewhere and then you can sell the building. You are liable to make a few hundred gold for each BP you cash in like this.