I like to keep certain things in mind.
1) Teleportation has a limit on weight, based on what the person/people going can carry. People aren't weight, they're the other limit: One creature per 3 caster levels, large, small, fat or thin.
2) Bags of Holding have weight limits. Exceed the limit and the bag bursts, scattering the contents across the Ethereal plane, "forever lost".
3) Bags of Holding are subject to damage if sharp objects are stored in them. Are any of the PCs wearing Spiked armor, or carrying unbated spears or pole arms?
Number one is the big one. If your caster is, say, 10th level, they can take themselves and three other creatures. Doesn't matter if they're under Reduce Person, stored in a Bag of Holding or riding on someone else's shoulders. Creatures never count as weight, and weight never counts as creatures.
Point two may or may not be a problem. In 3.5, a Type I bag has a weight limit of 250 lbs. and itself weighs 15 lbs. That's one hefty fighter, with gear.
A Type II has a 500 lb limit, and weighs 25 lbs. That's two fighters or three moderate weight people without geat (166 pounds each).
A Type III has a 1,000 lb limit, and weighs 35 lbs. That's most of a party.
A Type IV has a 1,500 lb limit, and weighs 60 lbs.
I ran a game once where the party found a magic bag. Rather than cast Identify, one of the players picked up his dice bag and a pencil. He explained, "I take my dagger and... he illustrated what he was doing to test the bag: He dropped the pencil in, point first.
I tried very hard to keep a straight face while I asked him what happens to a Bag of Holding when you drop a dagger in, point first.
What, you thought I was going to ignore my third point?