GoTo alignment

Excuse my beginner's ignorance here, but I have a couple of questions.

I have a Celestron C8SGT, and was aligning it. First of all, I left the
thing OFF, levelled the tripod, set the altitude scales to my latitude,
pointed it North, then used the altitude screws to make fine adjustments and
also the azimuth screws to bring Polaris into the centre of the view. I took
care to make the tube's axis be parallel with the mount's polar axis. So in
theory the scope should be roughly aligned.

Then comes the GoTo alignment. I turn the scope on, and it tells me to make
sure that the arrows on the mount for Dec and RA are lined up, and then it
asks for the preferred method. With a Quick Align, the results were
disastrous. I tried re-aligning, it made me point at Polaris, I did, and
then when I told it to slew to Polaris it went completely wacky. Then I
tried a 3-star align. I chose Alioth, Alkaid and Altair. I guess that my
manual alignment must have been good, as it took me to these pretty close
when asking me to center them. I then used the GoTo feature pretty
successfully with several stars. Strangely though, when I told it to go to
the Ring Nebula, it went almost 180deg out.

So, my questions:

- Is the GoTo alignment something different to polar alignment, or does it
have to be done as well as (after) polar alignment? In other words, if I
have the mount's polar axis all wrong and point the thing at the 3 stars it
asks me to during the 3-star alignment procedure, will it still work it out?

- Any ideas why the Ring nebula GoTo went so wrong?

- Why are the Dec alignment arrows on the mount not such that when aligned
the tube axis is parallel to the polar axis? They are about 20deg off or so.

Thanks in advance.

GP