I've been away for months from this game, took a break and waited for more and better mods. Now I fully reinstalled the game and feel like improving my game again, like I did before. Now I have a dilemma, the Dawnguard DLC looks pretty interesting but I haven't bought it yet. I noticed some mods are still incompatible, which is a shame. Especially Open Citites and Sounds of Skyrim appeal to me, but they don't seem to work completely?

So maybe I should skip the DLC for a while until everything is made compatible and just stick to the vanilla game and mod it as best as I can?

I use all my normal mods and Dawnguard with no apparent issues at all. I wouldn't even worry about it.

Sounds of Skyrim doesn't work, period. The mod author discovered a bug that bloats savegames in the last mod of the series, and took them all down. I use Open Cities and Dawnguard together myself, and so far I didn't notice any incompatibility between them, except maybe that vampire attacks won't happen in major cities. But it'd be better if they don't, because those get really annoying really fast.

I'm not aware of any other popular mod with compatibility issues. Dawnguard is more of a mod itself, and as such most mods didn't have to do anything in the first place, and those that did updated already (except Frostfall).

I guess I could live without Sounds of Skyrim for now. As it seems the other important mods I want to use do seem to work. Although I read somewhere that Open Cities had trouble with Dawnguard in Riften. I quote (from Skyrim Nexus comments): ""Appears to be incompatible with Dawnguard. I installed the mod and then uninstalled it when I discovered that going near Riften caused my fps to absolutely tank. (I downloaded off of nexus so I didn't see the proper uninstall directions, only some rant about gates). Reinstalled the mod some time later and tried uninstalling the proper way (interior cell far away from cities, save, uninstall, waited 5 days), no go. Brynjolf, Brand-shei, and a number of other NPC's in riften are in open world version and not in vanilla. I haven't checked the other cities. If it's Dawnguard's fault, being official DLC, you may want to make a notice about it's incompatibility since lots of people are going to have it. If I'm doing this all wrong and there's a simple fix for this, please let me know."
Until then I'm going to try moving every individual npc using the moveto command.".

Not sure if it's completely true or it's just a problem on his side.

No, I had the same problem when I temporarily deinstalled Open Cities, I just assumed that it had nothing to do with Dawnguard. I didn't have any problems with the framerate, though. If it's really Dawnguard thats causing this bug, it might be best to keep off of it for now after all.