1. NO
2. YES
3. NOW

depends on you, more phones are coming this Q3~q4 2013 like nexus5? iphone5s,5c? or iphone 6?, note 3, new htc one maxx (dunno name LOL). for me, i bought my s4 on the 2nd week of its official launch as my htc one s had gone crazy haha

for your questions
1 - always check before you pay for your device, and theres always custom rom to tweak your s4 
2 - 4G ? better get 2gb~3gb data plan or its not worth it
3 - in the end, its all up to you, like most our sifus said, there are no perfect phones in the world, theres only perfect phone JUST FOR YOU.

PeaceOfMind,

1) Some apps may crash on stock ROM, like mine. Changing ROMs have a chance to fix that.

2) Quad core is still future proof. Snapdragon 600 is not a bad one, although there's a faster clocked variant, Snapdragon 800 which is used for the S4 LTE-A

3) If you're in a hurry then by all means, purchase it. However if you wait for a while more(maybe around a month or less/ more), you can get your hands on the LTE-A(I9506) which offers both 4G and a better performance SoC(System on a Chip) than either I9500(3G) or I9505(4G)

1. Did not own the phone yet, so cannot answer.
2. If this S4 LTE still not enuf for heavy user...I don't know what phone still can cater for heavy user for now.
3. If you really want to save money, wait till Note 3 launch prob in September, price should drop. Then when Note 3 arrive at October or November, S4 price will drop even more......oh wait....when S5 come out next year, it will drop even even more, hahaha..

Honestly tho, I'm also waiting to buy but looking at price dropping fast and Note 3 gonna be launch next month (probably), I will wait to see how Note 3 design and specs looks like first. Then again, Note 3 is definitely going to be way more expensive, so not going to save money. So I suggest go for S4 if want to save money, no point waiting, coz price is not gonna stop dropping, never ending wait and postponement...unless you're considering Note 3 for its size (Just compared my S2 with S4 side by side, enhance size, yes but somehow.....only IMO, only slight increase in readability for me, getting old, so maybe have to wait for Note 3 to see if its gonna be too big due to prob size increase.)