Most of the higher magnification eyepieces are redundant when you have a 2x barlow so I can't say they're giving you a lot for your money on that part (using a 17mm eyepiece with a 2x barlow will give you similar results as using an 8mm eyepiece for example). I also don't know what quality they are from the picture alone but I would guess only slightly better or on par with the bundled eyepieces you get with your telescope out of the box. The color filters and moon filter are about 30 to 50 dollars for a bundle.
I would say don't get this, and instead invest in a decent low power eyepiece (30mm to 40mm) and a zoom eyepiece (something like this if you're on a budget https://www.amazon.com/Celestron-93230-24mm-1-25-Eyepiece/dp/B0007UQNV8) and a 2x barlow (https://www.amazon.com/Celestron-Omni-2X-Barlow-Lens/dp/B00008Y0TM)
With the zoom eyepiece and a 2x barlow, you can get any sort of magnification you want. Of course it won't be as good as a dedicated single magnification eye piece, but not having to switch out your eyepieces all the time will be very helpful. For the moon and wide views, the 30-40mm eyepiece will be nice.
Camera: For planets, you should get him an astronomy camera for planetary photography. Since he has the DSLR he can use that for DSO (deep sky object) imaging. Something like the ZWO ASI224MC ($200 USD) or the ZWO ASI585MC ($350 USD)
Telescope: Something like the NexStar 6SE ($1100 USD) would be perfect for planets, but not for DSO.
https://www.celestron.com/products/nexstar-6se-computerized-telescope?_pos=8&_sid=cf44af90f&_ss=r
Mount: If his main thing is planets, then the 6SE mount will be good enough. However, if he would like to go to DSO imaging, the mount will not work well as he would want an equatorial mount and not an Alt-Az mount like the one included in the 6SE. The AVX mount should be an excellent choice for him if he wants that mount. Celestron sells the AVX mount with the 6-inch SCT with is the same one as the 6SE.
https://www.celestron.com/products/advanced-vx-6-schmidt-cassegrain-telescope
Other things to consider: A Barlow lens will help a lot with planetary imaging as it essentially doubles the focal length (zoom) of the telescope.
https://www.amazon.com/Celestron-Omni-2X-Barlow-Lens/dp/B00008Y0TM
DSO: If he would like to do DSO imaging, then you can buy a Newtonian reflector designed for DSO astrophotography and it will work with everything above.
https://www.highpointscientific.com/apertura-6inch-f4-imaging-newtonian-ota-6f4n