Is there a limite to the resourcespacks size when we are on minecraft 1.12.2 ?
If yes, is it possible to load somes resourcespacks from a server ?
There are three limits to resource packs.
The first one is anything that increases the size from default will negatively impact the player's performance. For higher-end machines this may only be a few frames per minute (yes, minute), but on lower-end machines any resource pack size greater than default may start causing drop frames. While a minority of the player population, this is something to keep in mind if you're trying to make your server as accessible as possible.
The second limitation is on the size that Minecraft will allow the player to download automatically upon joining a server. Last I checked, the maximum size was 50MB. If you're making this for a server you should consider this the hard limit to your file size.
Beyond that, the final limit is for operating systems. A few older systems (including ones as recent as Windows 7) have a hard limit of 4GB for a single file. Anything beyond that will cause handling errors and can lead to file corruption, or the file just not being read properly. Honestly if your pack is this big you've done something HORRIBLY wrong and should reconsider your life.