OK, thank you all for advices. OK, I will switch drastic, only I presume, kibble must be soaked at the beginning as his tummy is not used to dry food and I have panic fear from bloat. (one of my saints died from bloat in my arms because it was saturday night and no vet available...It was 8 hours of h*ll for him, and for me, and now I am trying to do all to avoid such things).
Poop is not a big problem, our yard is about 12 acres, so plenty space for any poop. The only thing - I suspect that this saint is not housebroken at all and then it will be quite a fun
It is so much easier when I have people out here to ask for advice, it makes my mind on ease as I must think about so many things now - main thing is to introduce them tomorrow. My dogs like other dogs, only they can not meet outside, new dog must be taken stright into the house - and then it is accepted without any problems, instantly. Usually they say that dogs must meet outside, on neutral territory, but not for my pack. If somebody is invited in the house it means friend, and friends mean sharing bed, food or whatever from the step one.
But huge masculine dog may be a challenge for my boys... If he would be 10-16 weeks old baby, that would be so much easier.
My current foster Holly is eating with my dogs from one dish and it is like that - she goes to the dish, others step back to let her eat, and BArry, my alpha is supervising so nobody upset the baby. When Holly is full, then another two eat, Barry still watching, and then goes he, at the end. Very gentle and responsible alpha he is.