Hate to keep asking what might be repetitive questions but this is the only forum where I can get answers.
1) Giskards CURP 1.48 and DC's CURP 1.56 are they up/down compatible?
2) Giskards CUO and DC's CUO same question

3) As an aside has anyone tried Kvatch Rising and how does it compare with KA?

1) DC's 1.56 contains everything in Giskard's 1.48, and thus is backwards compatible with any mod requiring 1.48. This means you can use v1.56 from DC with any of Giskard's mods requiring v1.48. But you cannot use v1.48 with DC's mods as they may depend on things added since 1.48

2) I wasn't aware that there WAS a DC version of CUO. Do you mean the resource packs? They're all part of CURP, not CUO. The first six DC packs are the same as Giskard's six packs, so will work with all Giskard's mods. The additional packs from DC, so are not needed by any of Giskard's mods, but are needed by some of DC's mods.

3) Never tried any Kvatch overhaul mod, the only difference I know of is that Kvatch Rising does not rebuild the city stage by stage like in Kvatch Aftermath, instead it just pops it back into existence. Least that's what I've read.

Kvatch rising focuses on stages... But unlike ka... These stages focus on the logical regression of the city... The fires go out bandits... Nature reclaims it... And then is rebuilt...

These stages progress with he completion of the main quest...