The paint will rub away two times as fast if you don't wash the model before priming. Take care of the washed parts. You don't want to make them dirty again with fingerprints. Because it is much harder to do so. With single parts you can use a big brush and a big towel.
Assembled models have to be handled with much more care.
Now assemble the model. For plastic models I always use plastic cement. It holds much better than cyan acrylate. Show your models in action. Unbalanced models with arms extended look much more life like.