I understand you said you were new to SRK, but have you looked in the Doom Combo thread? The opening post has a 704,900 damage combo video in it. I’ve linked it below.
704,900: http://www.youtube.com/watch?v=12kCkw854cw&feature=player_embedded
Easier combo:
686,500: j.:f::h:, ADDF, c.
, c.:h:, :s:, j.
, j.:f::h:, ADDF, j.
, c:h:, :s:, j.
, j.:f::h:, ADDF, j.
, c.
, c.:h:, :s:, j.
, j.
, j.:f::h:, slight delay (for best results), ADF, j.
, Air Photon Array
939,300: j.:f::h:, ADDF, c.
, c.:h:, :s:, j.
, j.:f::h:, ADDF, j.
, c:h:, :s:, j.
, j.:f::h:, ADDF, j.
, c.
, c.:h:, Doom Time
I said in the last post; Doom has good reset options if you want to use them, but Doom is also very pretty capable of carrying people to the corner, so I rarely need to do his midscreen combos.