The specific things to watch out for, especially compared to GURPS 3E/4E, are super helpful! I figure the roleplaying part is the same regardless of system, that I'm comfortable with heh.
Thanks for the forecasts on 6E being well in the future - it sure seems like 5E is going gangbusters (oh, a TSR pun! Nice!), I imagine that has a lot to do with why this group wants D&D. The books are, of course, gorgeous.
Kind of scattershotting, but curious if expanding 5E to cover modern or even ultra-tech settings is feasible (or worth doing)?
One of the best things about running D&D again... I get to drag out those beautiful dice. I still have my first d20. It's closer to a marble than a polyhedral at this point (but I still roll it at conventions whenever I'm allowed to).
Reference - rarely played GURPS but I got years and years of HERO systems under my GM belt so kinda in the ballpark (bought lotsa GURPS product too.
At Drive-thru rpg you can find free basic rules for Edper Genesis which is a well done scyfy 5e system.
One fairly important diff between the GURPS/HERO model is the advancement. The level create significant jumps that cover a general advancement vs the small pieces of xp more common on point buy.
Another is the "heroic" gear accounting, where gear us "off the books" and so as GM you need to be wary of how fast you introduce powerful items.
Also, most levels are big but some are intentionally bigger. At level 5 you see a major uptick in power and the arrival of more than a few "bypass terrain and hazard" spells like (fly, water breathing) and the arrival of the more "quick kill mundane threats" like fireball. So at 5th level and beyond you will really need to step up the store of the adversaries to be more than just brutes in many cases.
At the lower levels, until you get handle on balance vs your party a good sort of encounter design is with waves of foes, not everything at once, staggered arrival with quick pauses sometimes for PCs to assess and maybe flee. Packs of goblins and wolves in the woods, alarms going off, hitting in small bands but getting more intense - sounds of more horns signaling etc - can really ratchet up tension and drama while not risking a single encounter tpk over a few bad rolls.
Finally, dont get hung up on hunting the right DC for tasks. One of the good references in the DMG suggests just using 10, 15, 20 with higher being no chance and easier being no roll. Use 15 for training **or** exceptional aptitude expected, 10 for neither, 20 for both. I often imagine "who set this up" and how did they fit on the training+aptitude+resources. Helps with quick and consistent rulings. Then let advantage and disadvantage play into more circumstantial modifiers.