Welcome to the shadows, chummer! (says the one relatively new to these forums as well
) The Sega Shadowrun was and is a personal favorite of mine (still have a Genesis with the cartridge hooked up to the TV in my office).
The back of the SR5 Core Book (381-408 "Helps and Hindrances") has a number of baseline NPC's, from gangers, to contacts, to critters for you to use in just such an eventuality. Since a good portion of the Sega Shadowrun is gangers, guards, and ghouls (oh my!) this should have you covered for the most part.
As for the matrix, you can more or less use the same topography from the Sega game if you want (there's a bit more nuance in a lot of 5th ed. Decking, but you can keep it as simple as that and go light on the rules- especially if it's your first time running a game!) The nodes in the Genesis Matrix all have a color and a number associated with them (like 2nd edition tabletop had). It's a little different in 5th, but you can use that number as the rating of the node (a rating 4 node would have rating 4 programs and such on them). The IC would be 'agents' (which are the same thing, but now lumped into a single category) that specialize in what they do (trace and burn, attack, etc.) Just follow the rules for that in the Matrix section of the core book.
Since the Sega game was based almost directly on the 2nd edition of the tabletop, the transition of it to 5th is not as hard as it sounds. It's more a matter of getting familiar with the rules and how they translate nowadays.
Hope this helps!
Crunch~
