Leave the bark on for a while and let it set on the ground if you want the outside to have a worm eaten look after you remove the bark. You say you're going to slit it. Do you mean that literaly or are you going to saw it? I like my mantals sawn 3 sides and live edge on the front. With size log I would shoot for 14" x 6" and get some side wood out of it. You could also get 2 half rounds, actually more like 1/3 rounds. Cedar is naturally pretty dry. Should be dry enough for your purposes in about two months.
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, Ford 851 tractor, JD 3032 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton and 2005 1 ton Dodge 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.