Well, most people usually beat Kyuubi with stamina, but you have Manda so you are going to have to do it with pure damage.
Your nins really need to last in this one. 4th, and 8th hits from kyuubi are always going to be 800+ damage so if you can get your first two gennins to take these two hits then its fairly simple damage vs. damage from there.
In your case though, well its going to be touchy. You can either pick up another summon and swap manda out just to beat kyuubi(will take more time too cause you will have to level that summon), or you can buy up some fresh pills and go LW hunting for stamina weps. You can put the fresh pills and stamina weps on your nins to try and get them enough stamina to get by while offsetting manda's abilitys