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?
#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.