use dragonmarks as feat, but eventualy allow them to be free starter feats. i dunno if developped dragonmarks justify full feats, maybe they should be level dependant level 6 and 12 instead for greator and major e.g.
Warforged is utterly hard to convert to 5e. Either you introduce repair spells or you do not but rule that they only get half healing, but in 3.5. they got so many goodies and immunities, cannot come up with a fast balanced solution. Maybe they get some of these but no HD to spend? maybe they need to use feats to enable these goodies?