on coinbase, I think you must first buy btc, then exchange there for ltc or eth. It's all on their site, so there's no need to do a bitcoin transfer. Then you do a transfer with the eth or ltc.
I think kraken may support direct fiat purchase of eth. They support euros, so probably a better choice for you anyways.
And vice-versa if you are going to fiat. You can transfer alt coin to your exchange, trade it there for btc, then get fiat for the btc.
Coinbase doesn't work for Germany.
Buying fiat with Eth sounds good tho. I will definitely check it out.
Thank you.