I'm creating a new character for Dawnguard dlc, to join the Dawnguard. However, I do not know which race I should pick! Any suggestions on what type of character i should play? Race, Factions and skills?

Imperial, companions, sword and board warrior.
Be my clone.

nord or breton, probably sword/range (for crossbow ) or sword and board. Although saying that my dawnguard character is sword/magic

Really any race would work. They seem the warior type though so i would recomend Orc, Nord, Imperial, or Redguard.

Go for an Orc beserker with two-handed and heavy armour. It's the most liberating experience to just scream at enemies and run in swinging an axe bigger than a cow. Try and develop a personal warshout as well, that always goes nicely; your neighbours may disagree, however.