Hey @alv_23, congrats on the 663M. Please share your in field experiences after you get to use them! Definitely make sure eye relief etc are OK/reasonable for you at the different zoom settings you care about.
If you do intend to use a tripod + head with your scope: I would not recommend the 128RC for this scope, primarily because of balancing issues. I own one and is such a pain. I would suggest going for something else that allows longer plates or better balancing (MVH500AH or something of that sort, keep the weight you want to carry also in mind). For the tripod legs, we have had no problems using a Gitzo 1 Series mountaineer (purchased used) for this scope. We have also used a Induro 3- series, an overkill I thought. I guess what I am suggesting is that you might not need the legs to be very heavy. You don't need to shell out on a brand new Gitzo / RRS when starting out as well. A comparable, budget friendly Sirui should do well! I know Marc (@marcsantacurz) loves his Sirui s.
For even better mobility, some experienced folks just ditch the tripod all together and go for a monopod (with a 3-legged attachment at the bottom), and are still happy with the performance they derive from such travel scopes! Just a few options to consider if you are looking into support gear.
For the photography kit, I did purchase the Kowa TSN-PA8 and a T2 Kowa adapter for fitting it to a camera. Perhaps they are both overpriced for what they offer. While we don't have cheaper alternatives that fit as well as the PA8, for the T2 adapters, I would happily recommend going third party for a fraction of the price. We have used third party T2 adapters on our other cameras as well with no problem, we don't find any difference in the output. In terms of what you can expect from this system, the output images are nice for recording wildlife at much farther distances. Of course, the resolution etc., won't be as great as what you can achieve with a DSLR + tele lens at much closer distances because of various reasons, the output is still enjoyable! I still can't believe we video-d wolves and bears of the Yellowstone miles away with such organic feel.
Cheers, and looking forward to your experiences! Enjoy!
Kumar