This could turn into a very long answer so I'll focus only on the part that I think is applicable to you.

.....you get a job that pays £18,600 or higher, you simply have to keep this job for at least 6 months,
then your wife would be able to apply for a spouse visa and join you - so in other words, you don't have to prove you earnt all £18,600,
just that you have a job that ultimately will.
Yes Aiden that's correct.

You would then apply under Category A after receipt of 6 compliant monthly payslips

Here's a summary of what UKBA state:-

With the current employer for 6 months or more

In salaried employment at the point of application and with the same employer and earning the salary level relied upon for at least the last 6 months.
Count the gross annual salary (at its lowest level in the 6 months prior to the date of application) towards the financial requirement.

Apply immediately after receipt of 6 compliant monthly payslips

Better not to worry about the other possibilities unless you have a burning desire to know.
I think it will confuse everyone.

Don't forget you can use any savings above £16000 towards any shortfall in earned income. (based on dividing such amounts by 2.5 - means savings of £25000 would equate to an earned income shortfall support of 25k-16k divided by 2.5 = £3600)