Buying your first fountain pen for many a year is not straightforward; many of the folks here are still searching for 'the' pen after many, many purchases. You've had some great advice and if I might add to the confusion, I would offer the following:
Buy a couple of cheap Chinese pens - I have bought Jinhao and Kaigelu (the 316) pens and they write pretty well, especially for the price. It gives you the chance to try out fountain pens, to try different shapes and sizes, and keeps costs down whilst you experiment. There is a great deal of information on here about Jinhao in particular.
Once you have a rough idea of the size and shape that you find comfortable, that may then help in choosing something which otherwise might prove an expensive mistake, or at least not exactly right for you.
Whatever you choose, I hope it works out well.