Hi Lin
Wonderful advice on the forum to your question, and its very tricky trying to decide what you want.
I am kind of with Carl here, that an 8" or 10" is great for a first scope. Gotos a good, but they are a bit fiddly, and you need to know some stars to do an alignment. In saying that too, you will learn those main stars very quickly , and find more in the night sky, if its working Ok.
Bigger the mirror = more seen, so an 8" which show you much more than a 4". My main starting scope was an 8" dob, and I had it for many years, it was great. i have an 10" Dob now that am happy with.
I also have a 5" GOTO which is still causing me grief - alignments, being level, facing south ......... can be frustrating. I am nearly there with it, but the Dob is easier!!
We have a viewing night at Donnington Airfield (Woodstock) next weekend 2nd July, that you should come to. We will have Dobs and gotos there,that you can look at and through. It is great to have a look at the set up of the scope and peer through the eyepieces. see what you like.
Look forwared to meeting you.