Anybody know if it is possible to get the paladin, m-11 wraith, and the black widow in 1 playthrough?

Actually you kind of have a choice, you ARE capable of getting ALL 3 in a single play through, i did it on my soldier, however as a trade off i ran out of money to buy all the full armors and was very limited in my ability to upgrade the rank of the weapons i had, though to help there are 2 intel items that grant a shop discount, one is found in the Asari Ardat Yakshi monastary and the other is in the Exodus Cluster Asgard system on planet Borr, each have an option for a 5% shop discount, get both choose both and get a 10% discount, then purchase from the Citadel, not from your ship.