Welcome Mtnliving... Nice truck... should be same as mine, just a shortbed.
1) That small 5er should be within all ratings for that truck.... You really need to get your truck loaded as if you were going camping... full tank of fuel, family loaded, all the coolers and other things you will put i the truck... Drive over a CAT scale and get the front and rear axle and total weights.
Your truck should be similar weights to mine, but you need your own weights are you are loaded with your family.
My truck wet and ready weights 7600 lbs. Limiting factor on these trucks is GVWR, so total weight of the truck + pin weight... Pin weight (at 20%) on that small 5er should be 1400 lbs, which would put you right at your 9000 lb GVWR.
You would be well under axle rating and well under GCWR. I can't imagine that truck having issues with that weight. My TT is very similiar in weight and it pulls like its not even there... Just watch your EGT's if the truck is chipped / has a tuner when making pulls up grade.
2) I don't have experience with the conversion hitches... however I am going to use the Andersen Ultimate Hitch when I get my 5er in the spring, after doing my own research... however I don't have first hand experience with it yet.
2014 Ram 3500 CCLB 4x4 Dually 68RFE, 370/800 Cummins 3.42 highway gear - Deep Cherry Red
2016 Coachmen Chapparal 360IBL
Sold - 2005 Dodge Ram 2500 SLT QCLB 4x4 - Cummins Power