The Preppy is the best for first timers. Platinum nibs are conistent and the cartridge/converter system is the most veritile of all the filling systems. It's a good baseline to gauge what you prefer.
I just can't recommend springing for the converter though. Platinum converters cost more than the Preppy. Their cartridges are sturdy and can be reused if you clean them out. I recommend picking up a blunt tipped syringe and refilling them with ink samples or from bottles.
Oh there are so many! Just pick a color or shade and there will be dozens that people swear by. Just be careful with shimmer inks since they can clog up the feed. They're fun and pretty but need a little attention.
I recommend checking out a few ink review blogs to find a handful to try. "Mountain in Ink" and "Fountain Pen Pharmacist" are two I follow. Places like Goulet Pens and Pen Chalet sell 4 mL samples for a few dollars which can last you a while on their own. Which is a great alternative to spending anywhere between $8-$60 for a bottle of ink.
As far as specifics: you can't go wrong with the Pilot Iroshizuku line, Diamine inks is another good one, and I think Sailor makes a lot of really nice ones.