Those are great choices. I think Cruise and Holloway are a tad too old for Apollo and Starbuck, though. Would've been perfect 15 years ago though. Might substitute Scott Eastwood for Holloway.
I think I would try to duplicate the success of the original series.
I'd pick rising, but relatively unknown actors for the parts of Apollo, Starbuck, Boomer and the rest of Blue Squadron- guys in their early 30s. Ditto for Cassiopeia and the other secondary/background characters. Secondary movie actors and soap opera/prime time character actors would be fertile ground for this. Maybe some of them of them held brief leading roles on TV like Richard Hatch, or starred in independant movies. For Serina, pick a recent Bond girl! Just like Jane Seymour! Why not!?
For Adama, I'd try to pick someone who had some gravitas; someone who had already played a leader- like Lorne Greene had with Pa Cartwright on Bonanza. Any number of actors in their early to mid 60s could pull that off. But here's a curve ball for you- how about Kelsey Grammer? Don't laugh!! He's been a comedic actor, but he's not a comedian. He's shown some serious acting chops in the past, as recently as playing the mayor of Chicago struggling with Alzheimer's in the television series "Boss." He'a even played a Starfleet captain in a ST:TNG episode. I think he'd bring the reserved dignity and warmth to the character that Lorne Greene did. If the bald head is too much for some people to get past, he could even stick a rug up there like Lorne did.
How about Seth Gilliam from The Wire and The Walikng Dead? He's a little young for the role, but would bring a deeper intensity to the stern, uptight Col. Tigh. Or maybe Jeffrey Wright of Casino Royal and Westworld would be a better fit for the role- for the same reason.
For Baltar, I would try to cast Gary Oldman. He would capture the mixture of evil and paranoia of the original character perfectly!
Both beautiful women! I could actually see Rebecca as Serina more than Gemma. I would probably focus on remaking Saga of a Star World first before worrying about casting Cain or Sheba. At that point in the story, they would've been thought of as dead.
The problem with Harrison Ford and some of the other big names mentioned above is that BSG is still seen in Hollywood as a "Star Wars rip off" or "too pro military" or "too conservative," etc. I don't think you would be able to draw them without huge sums of money (which would affect overall production value) or if a really big director with a "unique vision" were to attatch him/herself to the project (which would negate the attempt of a true remake). I only suggested Gary Oldman because he's done a remake before (Lost in Space)- which in all honesty might make him not want to do another remake, but the the lofty role of Traitor of the Human Race might make him change his mind.
I kind of based my casting on Marc Singer's model for the X-Men. Patrick Stewart was a well known, successful actor, but not a HUGE Hollywood superstar. Like Lorne Green playing Adama, he came to the Charles Xavier role with weight due to his Captain Picard gig. Ian McKellen was arguably the bigger name- just like Oldman would be to Grammer. The rest of the cast were either rising stars or no names at that point.