Lots of questions that I am sure you will get a lot of different answers for. An 8" SCT is a jack of all trades and many of us here have had at least one over our time in this hobby. You may find some general consensus in the answers, but some will be varied because of our experiences, budgets, and uses for it. There are dozens of threads already started about the questions you asked and I would suggest searching for them in the "cats and casses" forum, though you may find some here in the "classic telescopes" forum as well.
The best advice I could give you is to find your local astronomy club. I will guarantee at least one member there has one is willing to answer all your questions in person and show you how your scope works, how to clean it, how to collimate it, etc. Here is a link to find your nearest one: https://www.skyandte...-organizations/
I would not focus on imaging the planets right now. It has a learning curve and the planets are setting now. You should focus on learning how to use your scope before that. You also don't need a barlow with this scope. Collimation matters much more on this scope for viewing details on the planets than a barlow ever will. Your 8" also focal ratio of f/10 which means that you won't need a barlow because your eyepieces already take you to a useful magnification. However, it looks like you have a f/6.3 focal reducer on it currently. It effectively takes the scope from an 8" 2032mm focal length f/10 to an 8" 1280mm f/6.3. It screws onto the back of the telescope before the visual back and diagonal. Removing the f/6.3 reducer would essentially act like a barlow, giving you around a 1.6x more magnification. An f/6.3 reducer isn't a negative accessory though, it just lowers the magnification of your eyepieces and widens the FoV. In fact, for viewing DSOs (deep sky objects) the f/6.3 focal reducer is a great accessory to have and some 8" SCT owners keep it on most of the time.
The ONLY purchase I recommend to you at this time is a 1x magnification reticle finder. I recommend a Telrad. You find them on almost any telescope from a simple 6" Newtonian up to research grade observatory telescopes. Here is a link for a new one from this sites sponsor Astronomics: https://www.astronom...s-and-base.html as a member of Cloudy Nights you get a discount. You may be able to find a used one here in the classifieds for a little less. Simply attach the base on the tube of the scope with double sided tape and you are good to go. I use mine to get myself "in the neighborhood" of the object I am trying to find and then dial it in with the magnified finder. It will help you a lot just learning the sky. In that same vane of learning the night sky, bring out a pair of binoculars.
For eyepieces, I can tell you that your 26mm should just about live in your scope right now. Like you experienced, bad seeing will affect your view of the planets and your 11.5mm and 9mm will be too high powered unless your collimation and seeing conditions are. You may want a high magnification on some objects, but your 26mm combined with your f/6.3 reducer will give you a wide FoV (field of view) and help you find objects. For more on eyepieces for an 8" SCT here is a link to a very reputable company's recommendations: http://www.televue.c..._page.asp?id=97 Their eyepieces are premium and the price reflects it. I wouldn't purchase any eyepieces now, but after you get the feel for your scope and current eyepieces you may want to make some purchases. You can find cheaper from other companies, but their article describes what kind of eyepieces best fit the scope and you can go from there.
It can be very easy to get sucked into the gear and accessories, especially with a site like this, but get out there and keep observing. Experience is often the best teacher.
Congrats on the purchase!
Edited by mfoose, 04 November 2019 - 11:16 AM.