OK, some basics first.
All directors are equal, although your company's Articles (its rule book) could give one director a casting vote, so if you have two directors, you are both equally able to make decisions about the company. Your shareholdings do not influence your powers as a director. This is sometimes overlooked - if you don't want your co-director to have equal power to you, make sure your Articles give you casting vote, or better still, make the other person a company secretary and/or shareholder only and not give them the powers of a directorship - all you need is a disagreement in the future and the company can easily become damaged.
As for shareholdings, all shareholders of each class of shares are entitled to received their proportion of dividends. So if you only issue ordinary shares, say 80:20 as you suggest, then your co-shareholder is entitled to their 20% share BUT they may waive it at their discretion - however you can't force them to do so. It is probably better to arrange for their to be special classes of shares - for example "A" and "B" shares that carry no rights to voting nor capital distibution on winding up - you would have the "A" shares and your co-shareholder would have the "B" shares - then the board of directors can vote a dividend only to "A" shares or "B" shares without issue (Although you come back to who has the power at board level to approve the dividend payment!!).
To pay a dividend, you need a board meeting to authorise it, so you need a written minute of the board meeting, and you also need to create a "dividend voucher" evidencing the payment, so no, you can't deal with it at the year end, the paperwork has to be done before the dividend is paid.
As for company tax, the payment of a dividend doesn't affect the company tax bill at all. The company is liable to tax on the £12k profit (adjusted for any other taxable income or tax allowable expenses), payable 9 months after the company year end. At low levels of profit, the corporation tax would be 19%.
From a personal point of view, there is no additional personal tax on receipt of a dividend, unless your total personal taxable income for the tax year exceeds the higher rate threshold. The gross dividend (i.e. amount received divided by 0.9) is added to all your other taxable income in that year and any excess dividend above the higher rate tax threshold is taxed at a further 25% of the net dividend representing the excess over the higher rate threshold. So if with your dividends, your total income stays under the HR threshold, no additional personal tax is due.
Hope that helps.