Not sure how you are going to get yourself out of the Solar System, for some grand space opera, then.
That's one thing I've always found lacking in Arthur Clarke's stuff. He seems to have more or less rejected the whole concept of FTL travel, and so the "space opera" aspect is missing. Of course I've not read all of his books.
Star Trek's handwaving is probably the most egregious example. But Star Wars
isn't far behind, with its conflation of "light speed" and "hyperspace" and Han Solo's contention that the Millenium Falcon made the Kessel Run in 12 "parsecs" (yes, I know this was later retconned, but let's be serious, Lucas made a mistake). I guess Star Wars' setting makes the difference - it's not pretending to describe a future history the way Star Trek is.
For me, it's suspension of disbelief, so I can read the story. And I forget which SF writer used the axiom that you always allow one impossible premise in a good SF story, if needed. I always do.
As to Clark, I assume that whether it's mentioned or not, in such stories as CHILDHOOD'S END, there would have to be FTL travel. And somebody had to get here to deliver that monolith on the moon.
David Weber doesn't wave hands, the "theories" behind his FTL capabilities and restrictions are integral to almost every aspect of the Harrington universe, and his appendices are marvelous. But I doubt one could construct a functioning ship's wedge from them. Likewise , he's thought through extensively other scientific aspects, as in life extension, genetics and exobiology, utilizing, as many SF writers do, scientific advisors, as he once discussed with me.