For (1), the Mirai will use two 70 MPa (10,000 psi) carbon fiber tanks lined with a polyamide resin to give a range of approx. 300 miles ...

http://blog.toyota.co.uk/how-does-toyotas-fuel-cell-vehicle-...

http://www.plasticstoday.com/articles/toyotas-fuel-cell-car-...

A Toyota exec recently fired bullets at the tanks to allay fears that they would turn fuel cell vehicles into Hindenburgs waiting to happen ...

http://www.autoblog.com/2014/01/16/toyota-fires-bullets-hydr...

Firing bullets at it when the tank is new is just a publicity stunt. Those tanks need to be holding hydrogen for at least five years, all while being cycled from full to empty, then lets see how well they hold up.

On #1, energy density isn't a huge problem; sure, hydrogen is worse than gasoline in energy:volume (though much better in energy:mass), but its energy:volume is better than that of existing battery technologies -- this is one of the advantages FCVs have over battery-powered EVs.

#2 is similar to problems solved by Toyota's gas-electric hybrid design, and Toyota's Fuel Cell Vehicle's back to their earlier demonstration Fuel Cell Hybrid Vehicle version of the Highlander use a similar approach, with a battery to buffer the fuel cells output the same way that the battery is used in their Hybrid Synergy Drive to buffer ICE output.

On #1, it actually is a problem. Look at the range of the fuel cell cars that have been released or announced. None of them have even as much range as a Tesla Model S (and they cost more...).

It also presents a problem for refueling. There is no reason to expect a hydrogen car to refill any faster than a natural gas car (and plenty of reasons to think it will take longer to get the same amount of range). If you aren't familiar with natural gas cars, take a look at the Edmonds's long term review of the Honda Civic NX.

Frankly, I don't see how hydrogen cars are going to compete with electrics in terms of range, performance or refuuling time. Who is going to buy them? And we are subsidizing the hydrogen infrastructure, why exactly?

H2 is difficult to store. To store enough of it to be useful it needs to be either very high pressure or so cold is becomes a liquid. Because it is so small, it tends to leak through most materials and can cause them to become brittle (http://en.wikipedia.org/wiki/Hydrogen_embrittlement) but it is not "extremely corrosive". Thick carbon fiber tanks can store H2 at high pleasure so that with the efficiency of an electric drive-train, the car has good range.

On 2), the Mirai has a 1.6kWh battery. I believe the model is an electric motor driven by the battery, which is recharged by the fuel cell.