Is it possible to install mods with the original SE? (The Elder Scrolls 5: Skyrim)

no

This is not once mentioned. Impossible. Or the game will not run, or they will work very unstable.

if modders can optimize it

Vlad The Mackay__
You can, but there are shoals. If the mod is simple, it is possible to save using creation kit 64 and recode using sseTranslator. If the fashion of the nif files, optimize nif Optimization. But if the mod with the scripts, skse, then came here to wait for the skse 64 (promised in March) and when the authors of the remake of fashion with these scripts.

Vlad the Mackay__ wrote:
is it possible to set a fashion standard Skyrim Skyrim SE?
Can. But not all mods will catch on. Those who survive will work correctly and well. A lot of mods basics (the objects) installed in SE and everything works fine.

Rottan
and companions and the animation?

Some mods come with support for both the original and se, but you can find them again(roughly speaking there is a mod lockpick pro, you can download it for one version and another). You just need to find the same mod on se.

Metalist1925 wrote:
and companions and the animation?
I have not tried these. I'm interested houses, castles, objects and quests. Here mod the forgotten city (the quest) on SE not working. Had to install the legendary Skyrim version 1.9.32.0.8. Here mod installed. Now I have 2 Skyrim. ))) But the mod difficult to pass for me. Couldn't figure out.

You can - but with unpacked BSA files! I play normally go.