Line up the finder during the day, and then go out just after sunset and check out Venus and Jupiter. Look west; Venus is the brightest "star" at an altitude of around 25 degrees, and Jupiter is the second brightest at around 50 degrees. Jupiter will look quite small, but you should be able to see its moons and the two largest cloud belts using your 12.5mm eyepiece. Unfortunately you missed Saturn this year, but Mars is coming around.
The 40mm eyepiece is probably too long for the 25mm focuser to give a respectable field of view. The 4mm is likely to be totally useless with 0 eye relief. And unfortunately that 3x barlow is not going to go too well with either eyepiece. With the 12.5mm, it gives you 216x magnification, which is likely more than the scope is capable of, and with the 40mm, it gives about the same magnification as the 12.5mm.
The erecting eyepiece might work with the 40 & 12.5mm, but the image quality will be worse than through the 12.5mm alone.
If you have some old binos, you can pull the eyepieces out of them and use them with your scope. Check out
this thread.
