I tend not to buy priests unless I'm rolling in cash, which is unlikely. Someone asked if I use the second 1,000 for monks and the answer is no. I use that for a Vlemish Helm. If I decide to get high priests I will get them after I have purchased Vlemish, Nimroth, Unbreakable and currency. But you have to understand my Sedna style. I do not play as an assassin, but as a baiting tank. I don't even take Pounce 1 until level 10 or 11 because I'm not interested in killing other DGs. I want them to waste their time attacking and chasing me while my team takes a War Score lead. Meanwhile I'm throwing out 1,500 point heals at will to my teammates. Once we hit WS 8 I have the speed, armor and health to sail past any towers, lock portals and teleport out. I will pretty much always have the gold to buy creeps when needed and would definitely sell equipment to pick up cats.
Ironically, for other generals who cannot heal on their own so quickly, monks and priests are extremely important. They will pay for themselves in pots very quickly. In the end, how you spend your money depends on your play style. I may not help my team by having monks, but I will by getting currency the second we hit WS 3.
You say that try to play like a tank. Well thats great, because thats exactly what Sedna is supposed to do. And monks are by far the best item to help you do it. Sedna does not have infinite mana unless you spend a lot of money on multiple mana items, but you have gone to great lengths to describe how frugal you are with your cash, and how much you prioritize your health stack. If you plan to be soaking up all that damage, doesn't the prospect of getting a ton of free HP every 8.5s sound even a little bit enticing? How about a ton of free HP for you and another nearby ally, every 8.5s? How about all of that and some extra DPS? No? Well, newsflash. 900g for all that is a bargain, so much so that it completely overshadows any other possible combination of items you can get right off the bat. 1450g to double their effectiveness is also a bargain, albeit one that sometimes should be delayed until later, in favor of other bargains.
Also, my friend and I did some sandbox testing the other day, I've been meaning to convey the results to you. "Monk Sedna" (Heal + BotF + Monks) versus "Armored Sedna" (Heal + Banded + Scalemail + BotF). I played monks, my friend played armored. We met in the center of prison and wailed on each other until someone dropped. Somehow, he gained level 2 near the end of the fight, and at some point a minotaur came over from one of the lanes and started beating on me. I still won by about 500 HP. It should be noted that this direct, level 1 fight is the best possible scenario that Armored Sedna can hope for. Any cat and mouse only gives the monks more time to work. Any delay to gain levels and then fight helps monk Sedna more because increased max HP makes the monks better and the added healing power of Grace + Wind drags the fight out longer, giving the monks more time to work. What have we learned? Armored Sedna loses to Monk Sedna even under the most favorable circumstances, and only falls further behind from there.