For one of my group's arrival to Strahd's crypt... here's the pertinent info I had to bear in mind when putting together what was happening:
1) Strahd would not be in his crypt when they teleported in.
2) The group would get into the crypt via the multicolored stone brazier system that would teleport them in. Thus they would not have to face the wight-exchange teleport trap outside of the tomb upon entering.
3) Strahd's three primary female brides all have their graves within his crypt. Thus they were all viable candidates for antagonists when the party arrived. (And I did in fact have them resting in their graves when they arrived, and rose to attack when their graves were disturbed.)
4) The party had already destroyed the castle's Heart previously, and thus Strahd did not have that extra pool of HP that the Heart would absorb for him when he took damage.
Some other important things my game had were that I changed how sunlight affected Strahd and all vampires while in Barovia. While sunlight would cause damage and prohibit regeneration... it could not kill a vampire outright. Once a vampire reached 0 HP (in whatever fashion, sunlight or otherwise) they would turn to mist and return to their grave, wherein they were paralyzed for an hour in order to begin regenerating. Only by staking a vampire through the heart while in their coffin in this state could you destroy it. Thus it was not required for the party to attack Strahd in his crypt directly, they could attack him anywhere and only after he turned to mist would they have to make their way to the crypt in order to destroy him permanently.
Besides the three brides who could easily have already been in the crypt when the party arrived, Escher and Rahadin plus the Barovian witches knew how the teleport brazier worked and could get to the crypt if needed, I had several Helmed Horrors that paced and guarded the crypts on the whole that could engage the party, and bat swarms and wolf packs were also available to arrive as necessary (the HHs, wolves, and bats would not trigger the wight-swap trap.)
I had established a pair of teleport braziers at both the Abbey of Saint Markovia and the Amber Temple that matched the one in the Castle, so I knew they would be using that to get into the Castle to begin with. It turned out that they chose to port directly into Strahd's tomb immediately as their entrance into the Castle, rather than either of the other two castle locations (the Library and tallest tower.) This kind of surprised me, because they knew they still had to acquire the Sunsword from within the Chapel on the first floor. As a result, the three brides were there and attacked them when they arrived (before using the alcove within the crypt to teleport out once they began getting hurt). Then most of the group left the crypt up the stairs to chase after them and thus triggered the wight-exchange trap for several of them, while a couple of the PCs followed the brides via the alcove teleporter. They all had to chase after the brides through the castle before the brides were able to alert Strahd to the group's presence. Needless to say they did not stop them, and thus Strahd was alerted and the crap then hit the fan.
As far as what a fight in Strahd's crypt would be like... it would probably be like any other location. It's somewhat small and confining, no places available to hide (I personally wouldn't let the Rogue hide behind the stone slab on the far side of wherever Strahd is) and otherwise barren of items. So a fighter against Strahd there could be a little anticlimactic as was said above, especially if you have Strahd already having taken damage from the salting and burning of the bones. The biggest thing I'd say to remember is for Strahd to keep himself near the right teleportation alcove so that he could try and escape as necessary if the group really pounds him. Granted, his coffin is there so he'll have to come back to it eventually... but at least he could create a chase for the party to have to track him down to finally destroy him.
Hope that helped!
