A needle valve allows for very fine adjustments, (It's like a fine adjustment for a tap).
For the regulator, having the solenoid and bubble counter could be a good thing (upgradability, what if you decide you want a controller? or to put it on a timer? Perhaps even shutting it off during water changes?.. it's an easy way to turn it off)..
For pressure, I run mine @ 30PSI.
For upper limits on pressure (tank pressure). Co2 tanks are used for paintball, they blow a 1500lb burst disc if left in the sunlight, otherwise it's very rare for one to blow a disc (the burst disc is a failsafe to prevent the tank from rupturing, like a "overpressure release", but it dumps the tank.) so typical weather is OK, direct sunlight = extremely high chance of blowing a disc.
In either case, the reg in the first link is the one a lot of people have.. with no real problems. (other then forgetting to back the knob out before applying the pressure)