1) ClassiPress includes an advanced search functionality which is visible in the category view sidebar, so when a category is selected, the search can be refined further by custom fields selected by you. This is shown on the
ClassiPress demo site here.
2) You can create subscriptions which allow unlimited ads for xx amount of time and price determined by you, and also ad packages for individual ads. You can choose cost per category but ad packages do not apply and you can restrict categories to only subscribers if you wish.
The admin demo shows the setup for packages here. Money is not deducted from user accounts, as packages are paid for during the listing process.
3) Users don't run on credit, they pay for ads, but yes admin can determine if ads are published. Thanks.