Minecraft – Pixelmon shut down. Can I still play

Yes. If you change online-mode to false in server.properties, you can still play on that server while minecraft.net is down, since it doesn't try to check your username against the database. A word of advice, this will open you up to major griefing and it only allows one person to log in at a time.

You cant can't necessarily find weak pixelmon in a certain area, because the pixelmon that live and spawn in said area have randomly generated levels according to their current evolution stage and which pixelmon they are themselves. (Example: If a Weedle spawns In a plains biome, its level will be randomly picked from in-between 2-12)

My advice would be to do a lot of searching around for weak pixelmon to battle. If you still cant find any weak pixelmon, your you're better off creating a new world to play pixelmon in.