I think ideally you would want a team that plays in the same club/league/country so you get the best chemistry, as for formation its hard to recommend to some else as everyone has different play styles.
As you already have some good Bundesliga players you could start with Bundesliga team which usually consist of players form Borussia Dortmun & Bayern München (best players in Bundesliga). I would check out futhead.com and build a team so see that the chemistry you can get heres a team someone else made:
http://www.futhead.com/14/squads/8462595/
This is my current team its not worth 270k I am still saving up slowly but I found it to be a good start, the sub bench is the players i am aiming to buy. :
http://www.futhead.com/14/squads/8446028/