-Is it best to say subhan rabial atheem 10 times in each and every ruku? (likewise for subhanrabial ala in sujood, and rabbighfirli in sitting between prostrations?)

No, ten is not fixed. Once is obligatory and three is the lowest of perfection, and Shaykh Ibn Baz said five, seven, or ten is better. Praying alone there is no limit, but an imam should not burden those behind him, and the one following stays with his imam. Between the two sajdahs, rabbighfir lī once is obligatory and repeating it is better.