Hi John,
As Brian said, go for the 15mm eyepiece. A wideview one, even better!
I have a 4" dob and that's my most used and then I whack on the 10mm for planets.
The Andromeda galaxy shows up very well as does the Orion and Carina nebula. Take a tour around the area of the Southern Cross, there's a lot there to keep you entertained. You can view the brighter Messier objects such as the Lagoon nebula, some globs, I'd be surprised if you can see most of the Messiers tho
. Light pollution is a killer and there's a number of galaxies on that Messier list that I can't see with my 10" from home.
With the Sombrero galaxy, I struggled with my 6" and was only just able to make it out (from both home and a dark site). For galaxy viewing that's typically a nice bright one (awesome views in my 10"). So for my 4", I mostly stick to objects that are observable thru binoculars. Great for star cluster viewing. I have done a number of threads here on bino & small scope observing, maybe do a search?
I had a lot of fun touring Canis Major with my 4", so many gorgeous golden coloured stars. Point it to Wezzen and go for a tour around. VY Canis Majoris is easily nabbed, closeby is the Mexican Jumping Bean cluster and a nice colourful double.
As for the Pinwheel galaxy, good luck with that
, thru my 10" dob in light pollution it took me 6 months to find. I had to reach for extreme measures by using a large deep sky map with intense star hopping
. When I eventually found it, it was very obvious why it took me so long & I wish I hadn't wasted my time, I observed nothing else in that time as I was on a mission, but oh well, ticked that off my list. All that could be seen was the core, so it just looked like a star and only a hint if you looked hard enough of some nebulosity just around the core.
I then saw it thru a 16" dob from a dark sky, I still wasn't impressed though
.
Don't wait for objects to get too low, the murk in the lower atmosphere can muck with the views. About 30 degrees up I find is good.
For serious deep sky observing, a minimum of 8" aperture is generally recommended. Meanwhile, there's still a lot you can do with that 5".