Hi Adam
Lots of questions, not sure where to start
The 10 & 25mm eyepieces that came with your scope will actually be the focal lengths you will use the most. Anything under 5mm will depend on the seeing conditions (eg jupiter will look blurry). I found 7mm to be the sweet spot on planets. Within 6mths you will come to understand those clouds very well. This link covers are lot of basics you should know starting out, and in particular towards the bottom the page, atmospheric conditions are explained.
http://www.skyandtelescope.com/howto/visualobserving/
The Celestron kit does look good value. You will rarely use the colour filters (the blue will prob. be the most used). I got told they work best when planets are 60 deg up. Mars polar ice cap was visible thanks to the blue. They have their place in the kit even if used rarely. A nebula filter such as a UHC is a great all rounder. They make nebulas really pop out. Here is a link on nebula filters
http://pages.sbcglobal.net/raycash/filters.htm Here is a link on coloured filters.
http://sciastro.net/members/portia.p...use-of-filters Same with a barlow - I don't use it that often, but I'll reach for it on the odd times. By choice, I prefer less glass. The quality will be affected a tad with a barlow, because you are trying to transmit light through more glass. Hubby doesn't like the quality, where as it doesn't worry me too much. It's a trade off by getting the most value out of your eps.
Here is a link pretty much explaining just about everything you need to know about eps
http://www.optcorp.com/pdf/TeleVue/An Eyepiece Primer.pdf
Here is a link to a thread of mine (it will give you a good idea of the complexities involved with eyepieces/fov issues in eps with dob users). A very educational thread.
http://www.iceinspace.com.au/forum/s...ght=5mm+%24200
I have a Celestron ep, and it is of better quality than the ones that came with the scope. Wide field eps are a better choice for dob users in that you don't have to work the scope so hard in a small fov of 50deg. Also for example, I can view the whole Omega Centauri glob in my fov of 70deg at 10mm. You won't be able to do that with your 10mm ep. You will with your 25mm (but at lower mag). Don't worry, it will still look amazing. I can also use this ep to find things with, it's near impossible with 50deg fov.
Putting a 4mm (if seeing is good) on a dob can be frustrating as the planet only has to move a little before you have to nudge at the scope again (often losing it in the process and having to re-find). I find it difficult to observe a planet fully when I spend more time working the dob. You will get good at working the dob by the way. Wide fields therefore allow the planet to stay in the ep a lot longer. They also cost a lot more money because it take more glass and more groups to give you this view with maximum contrast and light transmission. A good widefield (Orion Stratus and Baader Hyperion, Meade, etc will cost between $200-$380. A premium will cost you around $260 for Panoptics at 19mm (Liz's favourite) up to $700. Second hand Pentax's & Televue Naglers generally sell around $350 ($500-700 new) with Vixen LVW's at around $250 ($330 new). Not many people will part with their Pentax's and Televue's. These eps are premium for a reason - they deliver the best contrast and sharpness across fov. Being widefield, this is more complicated to achieve, thereby costly. They knock a standard ep right out of the park! Once you have one in your possession, you will never go backwards, trust me. Pays to do your research on this eps, so that when they do become available on the second hand market, you will be ready to pounce straight away on what you want. That is how I've gotten mine. Patience.
Regarding viewing M42 (Orion). Use the 25mm. The 10mm won't do it justice as it will bring it up too close using too much of the fov in your ep. Nebs need a bit of distance to show up the contrast (wide field eps here again will give greater fov, so high mag is not an issue as you will see plenty of black sky surrounding the nebula). It's important that you get your eyes dark adapted for 15 -30(better) minutes before viewing nebulas. If you have to go inside, just put a patch over your observing eye or your hand. So as not to strain the unobserving eye, keep it open with your finger over the closed lid (or a patch). Within time, you will see a lot more detail. Your eyes will need to learn how to see the detail initially. The more you observe, the better at seeing your eyes will get. If you buy an observers book, this will help you look for details too as the book explains what to go looking for. A great observing book is Stephen O'Meara's "Messier Objects", I highly recommend it. It sells here i think for around $60-$70 dollars, but here you can get it for only $44 (free shipping) from the UK. I buy lots of books from here (so does Liz), there service is tops.
http://www.bookdepository.co.uk/book...essier-Objects
I agree 100% with what Ben said about learning the skies. Take it slow- you will learn quicker and won't seem so confusing. I find studying one or two constellations fairly well at a time helpful to me. The sky will always be there. And it is highly rewarding knowing your way around the skies. Soon the stars will feel like old friends when they return upon changing seasons.
Here is a link that will help you understanding what magnifications your scope can handle. Read beginner tips first, and then it will be a bit further down.
http://www.seqas.org/
Adam, please remember, it isn't all about magnification. So don't get excited about using that 2.5mm ep that Liz was talking to you about. At the end of the day, it comes down to the size of your mirror (the larger the mirror - the more light - the more detail you will get). With an 8" scope you'll have a whole lot of fun.
Plan your observing sessions - this will make your viewing time a whole lot more enjoyable and rewarding. Know what you want to see, get maps ready, scribble notes what they are you are seeing, get a comfy chair (important), a red light torch and you're on your way. My most frustrating nights are when I don't have a session planned. Organisation really does help. And also you feel like you have achieved things when you get those targets. Some nights when things are hard to find or things don't go to plan, I just aim my scope at a couple of easy favourites, and that keeps me happy and then go inside. I don't feel like a complete failure then! Main thing is, is patience. Lots of patience. If you don't have it (I didn't), you will end up having it (I did).
All the best Adam, have great fun!
Kind regards,
Suzy.