Empire can be the lifeblood of a Viking Clan. In the early stages of the game, the more property you control, the greater your income. A big income means the ability to buy or craft more and better inventory. In the later stages of the game it raises the price other Vikings must pay to put a bounty on you, and allows for buying more Counter Attacks, Bounty Traps, and Bounties against them. Spare cash becomes very important especially for those in a War Mode guild.
Investing your Gold in Empire will give you an hourly Income. The term hourly is used but if you choose the correct character type this can be reduced. For instance the merchant, has a payout interval of just 48 minutes.
Some Weapons and Warriors have an Upkeep cost, which reduce your net income. You should keep an eye on these numbers during the early stages. Many new Vikings end up unable to buy additional weapons or warriors because they do not have the hourly income to support any more purchases.
Buy your properties in as big a batch as you can (10) especially for the first few purchases.
Buying 10 at 100K will cost 1 million with the price for the next purchase being 200K.
Buying in singles the 1st will cost 100K, the 2nd 110K, 3rd 120K .... and the 10th 190K for a total cost of 1.45 million, 45% over the batch price. This difference lessens the more you buy but it will always be cheaper to buy in batches.
When you sell items you only get 50% of their purchase price back, when you sell properties you get 100% of their current price, but there's a catch. A similar thing happens to the sale price as when you buy, but in reverse. Selling in singles the price you get for each property falls by 10% of the base price so it is best to sell in batches of 10 as well.
Because it is possible to get 100% of your money back by spending your money on Empire this makes it a much better place to use than the Hoard. Even with the Fortune Hunter slot of your Elite Chieftains filled you still end up losing 2.5% of any amount you deposit. Having your cash stashed as Empire will earn you money and it also adds to your Bounty costs.
Empire properties have varying returns on investment, so buying equal numbers of each empire property is not the best strategy. An easy tool for tracking which property to buy next is salthefoot.com's Income Property Calculator