Synonyms for To begin with:

adv.

first (adverb)
originally, in the first place.
originally (adverb)
in the beginning.

adv

initially (adverb)
originally.
originally (adverb)
in the beginning.

n.

to begin with (noun)
earlier, originally, in the first place, in the beginning.

Other synonyms:

adv
in the first place.