Oh, you dont have to actually make them saints or say they are saints, of course.
Just prophet-like health and strength bonus (and minus) for the Bogatyr warriors, and holy magic for the national heroes with appropriate background, should you, of course, decide to make ones.
Bogatyr are not really saints except Ilya, they just draw strength from the home land they protect.
As for the reference to real historical figures somebody can see through.... the Three Bogatyr are absolutely free for usage
They are legendary heroes first and foremost. Make King Arthur a saint, people wont stop refering to him. Also, while Ilya the saint is known to be a warrior before he took up the wovs, and even his life really resembles that of a bogatyr Ilya, they are not officially aknowledged to be the same person.
Its just something people are free to believe (and usually do). And Peresvet isnt canonized, just a well-known and popular figure of a warrior monk.
And some more details (I just loved the idea, sorry for my persistance) )))
1) Early age - basically, what Bossuk said.
Awakened nature - talking animals, out of which bears are held in highest esteem. So yea, something about bears.
I liked the national hero Bossuk suggested. Michailo Potapych
Non-blood demons, including the Leshiy (forest spirit, not evil but hating these who harm forest), Kikimora (evil swamp hag) etc.
Some unique summons, or just national heroes. Likho the One-eyed, manifestation of misery cursing people, causing diseases and bad luck. Baba Yaga, old witch flying in a magical mortar with a broom, eating children and such but occasionally helpful. Zmey (wyrm) Gorynych, three-headed dragon spitting fire. No magic, just a reptile defying laws both natural and criminal. Koshey the Immortal, ancient lich who hid his mortality in a needle, very malignant. Sometimes shown as rather proficient with a sabre. Grey Wolf - huge grey wolf who's actually an enspelled Prince, helpful spirit known to join questing heroes.
Mushrooms... hmm!
Perhaps mushroom lore as some extra supply bonus and ability to cure diseases for nature priests?
2) Middle age - new faith.
Bogatyr warriors and heroes, priests of the new Orthodox faith, as in Pythium. New religion is spreading mostly peacefully, but paganism is disapproved strongly, main reason why there are no statues in Orthodox churches is because monks didnt want their flock to see anything that might resemble idols of old. Magi of the earlier age made less powerful in holy magic and have problems predicting the future. Their influence dwindles fast, last of the Magi are actually exterminated by force - somewhere in the end of the 2nd era.
For the priests, I'd propose an unique ability, like the reverse Inquisitor. Priests skill is considered +1 when preaching in a friendly dominion to make it higher. No effect in enemy dominion. Magic wise, since the religion has a Pythium origin, I'd make them in the theurges image, but with nature instead of water. For MA, 'high priest' is S2 N1 ?1, Holy 2. There's also a dean, just a holy 1 lowly priest.
3) Pithium fell, slavic nation barely survived the Horde onslaught, but emerged victorious in the end. Good idea would be to make two distinct slavic nations, one for eastern slavs, one for western.
Ruler of the Eastern one married the last Pythium princess (analogue of Sophia Paleolog), proclaiming his country to be the Third Ermor (hehe, Pythium being the second). Pagan traditions are all but banned - some of the creatures maybe be still hiding in the wilds, but mages dont have the skills nor desire to traffic in pagain superstitions. If the new God wants to summon them - he had to contact the pagan spirits himself, Magi are extinct. On the brighter side, Church proclaimed itself heir to Pythium Orthodox church, keeping the ancient litanies and traditions, so angelic beings can be summoned.
Most expensive mage/priests are S3, A1, N1, Holy 3, ?1. Maybe S2 A2 N1. Less expensive one is S2, A1, N1, Holy 2. Then its S1, N1, Holy 2 and an Exorcist with Holy 2. (After all its a LA, undead and demons are everywhere etc)
Troop-wise, cossac cavalry may be added in LA. Perhaps also streltsy, just with a composite bow instead of an arquebus -
http://en.wikipedia.org/wiki/Streltsy
Red uniform, two-handed Bardiche (like a halberd, but more suitable for parrying), ranged weapon. Not sacred, of course
Streltsy and recruitable bogatyr should be mutually exclusive in my opinion, though randomly appearing Bogatyr heroes are still present in any case, appearing time after time when the dominion is strong enough.
Nonhero bogatyr should be more properly named Vityas, to think of it...
Boyar cavalry, of course. Medium to heavy.
Also, in MA and EA holy banners are widely used. Standart with a face of God on it -
http://www.androsov.com/luvranyo/ermako.JPG
Boosts morale, some protection against the undead/demon.
P.S.
Another suggestion for the slavic priest/mages of LA -
To think of it, there's no justification for the official priests to have nature magic as a guaranteed pick. Just Astral and Air (study of God in Pythium tradition), and some random.
But there's a good reason to make two different types of priest/mages -
http://en.wikipedia.org/wiki/Old_Believers
The Old Believers were prosecuted, so oftentimes they settled in the wilds, minimizing (and sometimes even losing) any contacts with the outside world. These can possess decent knowledge of Nature magic, like N2S1 Holy 2 for example, no random pick.