Where can I find the rules for hiring/upgrading a crew for a ship? And where I can find maintenance fees?
The quick answer, I'm afraid, is that you can't. Neither the Saga Edition nor its predecessor produced any rules for starship maintenance costs or crew recruitment/training (at least, none that I can find.)
My suggestion would be to handle it as a story element - the players announce their intention, and the GM comes up with a scenario to help them achieve it. For example: they want to hire new crew - turn it into an adventure where the characters visit a station and run into problems such as crew unions or a corporation trying to monopolize trained labor. Maybe a Hutt wants all the best-trained crew for his new venture, and is strong-arming anyone else who tries to hire them. The players deal with the situation, and they get their improved crew while the actual cost aspect is glossed over and sits in the background.
Maintenance can be handled in a similar manner - a good example here is from Episode I where the J-Type develops a fault and they end up having to barter, gamble, and help an NPC win a podrace in order to get the parts they need.
It's worth noting that there's also no trading rules, and that similar story-orientated methods could be used here too.
While this may not be the answer you were hoping for, it's something worth considering unless you want to develop your own tables of fees.
Alternatively - it costs whatever the GM wants it to cost at the time, depending on how affordable they want to make it for the players. Supply and demand can cause price fluctuations far above what we're used to when you're looking at it on the galactic level - the only available navigator on the planet can pretty much name their price, as can someone that's got the very last replacement drive unit - and maintenance costs are also driven by what happens to have broken recently (which again, tends to be a GM call.)
(Edit) A more thorough check turned up refuelling, consumable restocking, docking and repair fees in the "Scum and Villany" book, in the Spaceports and Shadowports section of Chapter 3: Fringe Campaigns. There's also prices for hiring mechanics in repair bays, but this still depends on some GM fiat to decide what needs repairing and how long it'll take, and seems more aimed at having modifications performed (so, adding in that smuggling compartment under the deck and fitting military-grade weapons to your cargo ship.)
If you wanted to aproximate the cost, you could probably treat credits as close to a real life currency. I am basing this on trade goods listed in the core book. plain crew that cna push buttons for you would maybe be hired on for 500 a month, pilots 1500, techs 1000. Your ship's consumables would be feeding these people as well and needing replenishment.
I think because you can make a game credit lean or creditheavy you may adapt the costs on your own. In one game the docking fees were hurting players and in another the players were laughing at the costs and throwing 10,000 credits at a casino for the night.