The hotkeys take a short while to get used to; though if you're playing many other games, and not smashcraft all day (like you should be doing :3), you could easily be mixed up often, reverting to the former games you've played.
NEVER make a game more easier than it should be. The fact that the a class/hero is so difficult to use is its selling point for many; people will try to master this hero, deem it as their own, and build a competitive connection to those with equally difficult heroes. On the other side of the spectrum, people will deem it pointless that their innate abilities don't match up to those around, while others will be crushed just as soon as they get the hand on things, causing them to /ragequit. Simply, a hero that takes a whole lot of skill to use, but causes massive amounts of damage, is badass; some will try, some will fail, and some will succeed. Making it easier for one portion of the players isn't going to satisfy the whole of the playerbase. It's very possible to make everyone happy, though it requires either a lot of intuition, or a lot of knowledge to create that effect. ;3
A time limit is a viable option; as earlier stated, 5 minutes would be perfect for matches with a kiting healer, Sarina vs. Sarina, or Ezzerat vs. Ezzerat . Having the outcome based on remaining health will take out many of the mechanics and connotative ties to what makes a fighting game enjoyable in the end.
Agreed about fog of war; It would definitely enhance gameplay and require more tactics to function. Randomness is a charm for players. Allowing them to choose will make them see how many maps there really are, increasing the need for more maps; there needs to be a sense of mystery, background, and certain aspects uncontrollable to stimulate the feel for the game. Allowing choice will have people wanting to choose what their abilities are as well ;3.
About Sarina. One way to balance her is to allow a healing cap; however, that would cause disappointment for many people who seek to rely on healing (pretty much a foot to the face). Another way is to have many more abilities that work in different ways that require you to time them accordingly, pulling off chain heals; this would be a bit too complex and would require a lot of planning, however. Another way to balance her is to adjust her current heals to be more based on skill, than on healing output.
Here's what I have in mind:
Channeled Healing: Channeling is a horrible burden, in general, but to a healer who has nothing else to do but heal, channeling isn't a burden at all. To fix this, you could either make using other abilities more worth it, or you could make the ability work only out-of-combat. Instead of a channeling heal, you could have it be a bandage-type spell that is only maintainable on one ally at a time (not self).
AoE Heal: Good, as long as there is a spell-cast time.
Emergency Self-heal: Most medics use this as a self-heal in general, even when there is no control effect on them at all. Allowing it to heal only when a buff is canceled would balance it a lot more.
Ultimate: Considering how each ability is, or is about to be, this ability pretty much is the most balanced ultimate for this hero.