Important thing will be to contact the managers that have NT players /or candidates asking them to train certain skills that is the most needed for National team. It's always nice to see, that someone really cares 'bout your player and it motivates a lot (at least It always worked with me).
Tactics.. well, hard to answer this questions without knowing the skills of all the players, right? ;) Anyways I have no complex in choosing tactics and every decition will depend on a certain situation. But I'm not big of a balanced offence tactics fan, tho (I dont think that those works g8 against good m2m defence), and I'm still not 100% sure how isolation/box&1 tactics works, so I probably wont use something like that in key games.