Yes, you need to be invited to apply once you go through Skillselect.

Go talk to an agent, the first consultancy is free and he/she can explain the whole process for you before you decide to do it yourself or through an agent. Alternatively there are plenty of resources on the web explaining the process as well.

i will suggest you to go to agent for a free assessment...then u can decide whether to use them or diy..

if im not wrong, u need to pass your IELTS with the desired band, then only u can apply as it will determine whats your total points for the skill select for primary applicant, secondary applicant, i think u have to take the test but u just need a lower band.. both of u only need to take the General training..

again goto an agent and ask.. normally they are able to give you answer..

or goto other australia migration forums and ask..(google and find)

dun expect spoonfeed here :-)  as mentioned by other the rules changes every year, not everyone will be updated with it unless someone is applying for it..
and many of us already got our PR years ago, and the rules are totally different already..

like for my case, i can apply for the PR and take the IELTS exam later (as in before the case officer assigned) and submit the results when my file is assigned to a case officer which is 6 months later...but now u must submit the results with the application.. so google and do lotsa reading..

again, im not sure is there any SOL list anymore (if there is im sure nurse will get additional points) if not, then u have to be the primary applicant since u got more points..

i would prefer PR and look for job if you are certain you wan to live in Aus permanently (if you got kids, then u need to have enough money to survive while u r looking for job) But if you just want to try and work in Aus, yes work permit can be your shortcut, but as you mentioned there are risks, coz if they decide to fire you, u need to leave the country in a month time unless u can find another employer to sponsor you.. and the rules might change along the road for these permit.. as now the government is tightening the 457 visa ..

there are pros and cons for both option, you need to weigh on your own which one suited u (n ur partner)