His own generation (idiāi geneāi). Either locative case, “in his own generation” or dative object of hupēretēsas (served).
The counsel of God (tēi tou theou boulēi). So here, either the dative, the object of hupēretēsas if geneāi is locative, or the instrumental case “by the counsel of God” which again may be construed either with hupēretēsas (having served) or after ekoimēthē (fell on sleep). Either of the three ways is grammatical and makes good sense. Koimaomai for death we have already had (Act 7:60). So Jesus (Joh 11:11) and Paul (1Co 15:6, 1Co 15:51).
Was laid (prosetethē). Was added unto (first aorist passive indicative of prostithēmi). See the verb in Act 2:47; Act 5:14. This figure for death probably arose from the custom of burying families together (Gen 15:15; Jud Gen 2:10).
Saw corruption (eiden diaphthoran). As Jesus did not (Act 2:31) as he shows in Act 13:37.