Assuming you are using the Shorter Schedule of Cost Components then your understanding is correct, the CECA rates are used adjusted by the % in the Contract Data. Item 22 only comes into play when the Equipment is not in CECA (even when you have a rate in both). You are also correct that if you had neither rate then item 27 comes into play and open market rates are used. All of these rates would also attract the direct fee percentage on top.
Finally, again you are right, if the plant is brought in specifically for the work then you're back on actual cost the same as in item 27.
Finally, again you are right, if the plant is brought in specifically for the work then you're back on actual cost the same as in item 27.