Paul
The 25 and 10 will be plossls. You will notice that when you pop the 10mm in, the image will be larger, but it will be harder to see the image as eye relief is smaller (you have to get your eye closer to the EP) and the exit pupil is smaller. Also it will be a lot finickier (is that a word?) to focus.
When I had the 8" dob I used the 10mm about 6 times in 6 months, the 25 will do most things.
Try to get yourself to a club observing night or Star Party so you can see different EPs and how they work. You can easily match the money paid for a scope when buying EPs, I know my collection is easily worth nearly twice what I paid for my scope now! So you need good info to make the correct decisions.
Having said that, the 25mm you have is usually a pretty good one considering it is essentially a giveaway by the scope maker, so use it and enjoy the night sky.
If you are serious an 8" is the perfect starter scope, you will immediately notice that deep space objects are much easier to see and there are 100 Messier objects and lots og NGC objects easily seen with an 8.
Malcolm
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