Po. See on 2Co 10:13, 2Co 10:16. Emphasis on rule not this.
Peace be on them (εἰρήνη ἐπ' αὐτοὺς)
The only instance of this formula in N.T. Commonly εἰρήνη with the simple dative, peace unto you, as Joh 20:19, Joh 20:21; Rom 1:7; 1Co 1:3; Gal 1:3, etc. In the Catholic Epistles, with πληθυνθείη be multiplied. See 1Pe 1:2; 2Pe 1:2; Jud 1:2.
Mercy (ἔλεος)
In the opening salutations of the Pastoral Epistles with grace and peace; also in 2Jo 1:3. In Jud 1:2 with peace and love.
And upon the Israel of God
The καὶ and may be simply collective, in which case the Israel of God may be different from as many as walk, etc., and may mean truly converted Jews. Or the καὶ may be explicative, in which case the Israel of God will define and emphasize as many as, etc., and will mean the whole body of Christians, Jewish and Gentile. In other words, they who walk according to this rule form the true Israel of God. The explicative καὶ is at best doubtful here, and is rather forced, although clear instances of it may be found in 1Co 3:5; 1Co 15:38. It seems better to regard it as simply connective. Then ὅσοι will refer to the individual Christians, Jewish and Gentile, and Israel of God to the same Christians, regarded collectively, and forming the true messianic community.