1) Internal storage is not really the way to go anymore. They put 10GB interfaces on there for a reason. Sure you can spend hundreds of dollars to shove storage into the box, but a nice NAS provides you storage that is accessible from ALL your devices. Downloading and streaming stuff from my Synology to my iPad/Apple TV and Mac is worth way more than overpriced, non-redundant internal storage will ever be.
2) Nothing you described requires more than the base number of CPU's, if they had a 4-core model I would have bought it. Memory speed is something that only people chasing seconds or benchmark scores will ever notice. If you have to ask if you need incremental speed, than you probably don't need that speed. A couple of seconds shaved from something you are doing a hundred times a day adds up, but a very very small number of people fit in that category, and they know who they are because they suffer no matter how fast their box is.
3) The machine is beautiful, silent and will likely provide long term value. Trash can Pro's still have value, hard to imagine the new Pro won't hold similar or better value down the road. The biggest question is what happens when Apple pivots to ARM, but it would be hard to believe that the new Pro wasn't designed with that pivot in mind. Even if this is a dead end it will likely suffice for 3-5 years, which is a good return as long as you don't go crazy on the specs.
Remember, the whole point of this machine is that it can change. front loading the performance before you even know you need to defeats the purpose. If the CPU is slow, you can live with it for a while and in 6 months CPU upgrades will be that much cheaper. Memory is trivial to add. PC focused Graphics cards will start picking up support, companies will start porting PCI based stuff as it will all be low hanging/high margin fruit. Spend as little as you can for as long as you can and you will reap the rewards.