Well, the mace with scepter could easily changed into another simple weapon (or martial weapon) of your choice. Considering as devil you got brands involving Belial and Fierna, as outsider you got martial weapon proficiency you could wield glaive or ranseur as weapon which also supports your warlock EB's (also fits for pic your going to use for imp which has spear/polearm).<br/><br/>Now, cheap AC with no ACP would be mithril +1 chain shirt, for 2,100gp. Then remaining 4,500gp could go for a wand with any 2th level spell on it and 50 charges (or two wands with 25 charges left). Anything save based could be weak (having low save DC). But some buffing wands would work fine like invisibility (not yourself but on allies). Or cure moderate wounds to help out with healing. Or even hold person with save DC 13 can be handy against foes with low will saving throws.<br/><br/>The UMD check needed is either 23 or 24 for spontaneous casters (sorcerer/bards). So need 13 or 14 UMD modifier as warlock you can take 10 to UMD checks by now (if got 4th level as warlock). As otherwise you would need to roll or invest to UMD skill boosting ring.