Dave,
The best stuff I have ever used on the leather is a product call Leatherique
http://leatherique.com/. It's kind of expensive @ $55.00 for the 32 oz set (price has gone down, was $75.00 when I bought it last) but it is worth every penny. The only negative it that it is a two step process and to do it properly it will take a few days but ,again, it is worth the added work.
I haven't used the SSR 2.5 but if I remember correctly, that is a pretty agressive polish. You will want to follow it with a Final Polish (I think the Poor Boy's product is called SSR 1.0)
You really, really sould get a PC orbital to do all the steps before the SG. You will not be able to duplicate the speed or consistience needed on the polishing steps by hand.
Also, be very careful with the Klasse SG. You will want to moisten the applicator first and use a very, very small amount of SR (like 1.0 oz. for the entire car) Apply to a very small area ( like 2 ft X 2 ft) and then wipe off. If you can see the SG when you are applying it, you are using too much. When you use too much, it will haze up and the only way to get it off is to go back to the AOI and start from there again. If you put on more than one coat, you need to wait 24 hours before then next one to allow the first coat to cure.
The P21S is a great wax but does not last that long. It may react badly with the SG (haze up) but since your car is silver, I doubt you will have any problems.
Looks like you picked some great products. Good luck.