Base iMac good enough?

I need some help guys. I do some moderate photo (Lightroom 5, iPhoto, little bit of PS, Photomatix) and video (iMovie) editing for work, and our computer also doubles as a TV for online shows. We do want to be conservative price-wise because we're saving up for dental school. We'd like the computer be a little ahead of the curve, as we do not intent to buy again for 4-5 years, and we need the technology to last. So, with those things in mind, I have a few questions:

1. Is the base model 2013 iMac sufficient to handle those programs without stuttering? Is the Iris Pro graphics card good enough to handle LR/iMovie and simultaneous online shows? (Our last iMac struggled with online shows and editing software being open simultaneously.) Will 8GB RAM be enough?

2. If the base model is not sufficient, what is a must-have, definitely-worth-the-extra-money upgrade for our usage/purposes?

3. I've read mixed reviews on the Fusion drive. Good option and worth the extra $ for those who have actually used one? (Again, I don't have the money to go and buy more storage with USB 3.0 or Thunderbolt. Got to make due!) How does migration from Time Machine work with that? Do you have power to arrange files on the flash or HHD as you see fit, or do the drive think it knows what's best and does it for you?

4. If it's absolutely best to go strictly SSD, we need to reboot ~750GB of stuff to the computer (we have a 1TB external USB 3.0 HD as a Time Machine backup). Where can I find a good resource to migrate the important programs to the SSD and leave the rest to the ExtHD?