Hi DDJJ
(1) You need a T ring ($40) and a two inch nosepiece ($30). Take off the lens of the DSLR and put in the T ring. Screw on the nosepiece and plug it into the ED80 focuser.
(2) The filter can screw into the nosepiece. Astronomic make good LPS filters. You may also need a UV/IR filter to stop star bloat. Neither of these are immediate requirements, though without the LPS you will probably be limited to 2 minute exposures.
(3) I was using a 70mm Saxon achro as a guidescope. This is fine for widefield imaging with the ED80. These can be got for about $100 if you look around. A better option would be an Orion Short Tube guidescope.$218 from Bintel.
https://www.bintelshop.com.au/welcome.htm. Q guiders are great but a 2nd hand Meade DSI ($100) guiding through PhD would suffice as well.
(4) If you can afford the difference I would get a EQ6Pro. At Andrews they are only $1700 which is not much more than the HEQ5 Pro. This would be far more stable.
(5) Other things. Not immediately required but you will need a Focal reducer as initially you will find you get field curvature. You can crop this out. William Optics sells a good one for a few hundred dollars and they can be ordered quite cheaply from OPTCORP.COM.
(6) You will need some way of mounting the guide scope. I got two 'Guan Sheng special dovetail mount adaptor - FF561' from Andrews $49 each. These fit on each end of the dovetail.
(7) You will need a 24 amp hour battery, say from supercheap auto.
(8) You may need two heater straps from bintel to stop the scopes from dewing up. If your camera dews up, literally put a sock on it. Obviously you cant do this with your scope
You can get pretty close to the Zenith. There is no problem with the mount. More of a problem is the scope and camera which may get in the way when pointing straight up. As far as dust is concerned. You dont get much and if you do you can clean it off with some cleaning fluid available from Bintel. A little bit of dust is no problem. Definately dont clean it after each imaging session and just keep the plastic cap on when not in use.
Paul