I know the remaster for PC is free. Is it going to be automatic? If so how will that affect the mods? Especially SKSE mods.

Already spent hours setting up mods on my game and don't really feel like doing that again.

All mods must be opened and saved using the new CK. That's the minimum requirement. It's up to mod authors to make their mods compatible with SSE.

SKSE and all plugins using it must be remade, more or less. This is a much bigger task and may take some time.

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If you have now a working set of mods for standard edition of Skyrim, don't rush with the SSE. It'll be a while before one can use the same mod setup with SSE.

You might be able to have both versions installed. So you can keep the old version of Skyrim with all the mods and maybe play the enhanced edition in Vanilla mode.

SSE is a seperate "game" so you can keep your existing 32 bit Skyrim and also install SSE separately without affecting your existing Skyrim setup. That's what I plan to do, continue playing my existing modded game while tinkering a bit with SSE and eventually building a new load order for SSE as mods become available for it.

I likely will not use the 32 bit version of Skyrim and likely not use any mods for the most part. Maybe a mod here or there depending on the character that I play.