Thanks for your question.
There are no numerical thresholds which you have to meet in order to be eligible for a fiance visa (and a spouses visa thereafter). The standard you have to meet is, as you say, that you will have to support and house yourselves and dependents without the need to access public funds.
This means that you must be able to show that you have sufficient assets and income (both you and you fiance) that the will meet the expenses of day-to-day costs (food, bills, clothing etc) and the amount you spend on your accommodation (eg rent or mortgage). Obviously this varies according to , yes, the amount of dependents you have (ie., day to day expenses go up) and the cost of rent/food etc in differing parts of the UK.
In your application you should make it easy for the UKBA to grant you a visa by outlining a realistic budget for the expenses above and evidence of your income and assets. If your wife is to work here but does not have a job offer then you should show a list of available jobs that she could do and perhaps a letter from her current job stating her skills an experience. Similarly you should do this for you.
In the end it's about presenting a reasonable case to the UKBA that you will not be a burden on the state.
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