I'm a player turned GM (recent) and am working through similar questions. Originally, I thought winging it would be fine -- which for certain GMs can work. I've had some great roleplaying with GMs flying by the seat of their pants. But in those cases, it was a well developed world that they were drawing from.
For myself, I'm finding, writing up a summary of a "Behind the Scenes" is working fairly well. I don't design maps, but do upload reference maps from the web (google search is your friend). We use roll20 and have been pleased with it - they just did a pretty major update that included default character sheets -- SR5 is an option

-- and like it pretty well. I launch the campaign in Hangouts and run an online session.
Ultimately, I've found the more planning you do, the more smoothly the games goes. Kinda like real life! (So, would that be life imitating art?) I write an overview of the run, a cast of major characters - including some motivations, also some possible plot points that occur due to specific actions. What I have found that I need to start doing: lay out matrix/astral overviews; have a brief summary of legwork information and a timeline of when things happen.
I would suggest not going to the extreme of planning either, though; the plot is going to shift and flow.***"I know there is a balcony there--but it's fraggin' eleven stories!" / "Huh, your Parkour's that high? Hmmm....well let's see <roll, roll, roll>" / "Well...yes, you did roll well. <crumples sheet of opposition, and tosses over shoulder>"***

Still got a ways to go, but each session we play, it gets better and more interesting for both me and my players.
Keep in mind that (at least IMHO) it really helps to be flexible. The players never do what you expect; which ultimately is a good thing!

So to summarize:
*Planning good!
*Reference maps good!
*Flexibility good!
*Mini-Drone explosives goo....oh, did I write out loud again?
