You'll definitely want Freon AC and the Aft Baggage mod.

As far as DOCs...these are rough for a Citation II (Conklin shows a higher figure, but this is very close to what we experienced):

180gph average burn
$250/hr for engines
$250/hr for maintenance (parts & labor)

We cruised at FL360-390 for flights about 550nm+ in duration and 1200/900/850 seemed to work pretty well for fuel flows; if you cruise in the lower 30s expect to see roughly 1300/1100/1000. In the upper 30s 350-360KTAS is all you'll get; in the low 30s expect 370-375 KTAS.

Our airplane didn't have the gross weight increase, so 13.3k was our MTOW and our airplane couldn't top off tanks even with no passengers. At that MTOW, and using 185kt to 0.47M, then 500fpm the last 2000' to level-off for climb profile, you'll get to FL370 in roughly 30 minutes. It'll take you roughly 10 minutes to accelerate to ~0.60M if at 104.0 N1 MCT, and by 20 minutes after level you'll be at 0.62M...which is all you should expect in the upper 30s in a Citation II.

Longest flight I did was SAT-HXD @ 931nm great circle with two pax and bags for passengers & crew. Blocked out with 4400lb, direct (slow) climb to FL390, and IIRC we landed with 1100lb. Obviously if your airplane has the Branson/Newflight mod your fuel/payload capability will be greatly increased beyond what we had.

Assuming a ZFW under 10,000lb (which in our plane was two crew and 5 200lb passengers plus baggage for all), the New Flight mod would let you block out with full tanks...which should let you make 1000nm trip with IFR reserves and a <100nm alternate against all but maybe winter headwinds.