So a while ago I started a solo druid play through in MM7. I've chose to go with the light side and have gotten pretty far. I got stuck on the quest to kill Tolberti and was wondering if anyone has an experience for fighting him with one person with no grandmaster protection from magic.

For this case, people recommend to get Body Resistance buff in The Maze (you can temporarily raise it there to 255), and use NPC with town portal to go to Pit. And also use Luck Boost potion with high power, because Luck helps against negative status effects too. It will greatly increase your chances to survive, but some reloads might be needed.

Good idea. I wonder what about a solo Ranger... It should be far more though..

Without spell power, yes.

Question: does XP get multiplied by 4 when you solo? i.e. do you get the xp that your 3 companions would have gotten otherwise?

Yes you get full XP from monsters all by yourself (so 4 times more than in party) and thus level faster. However, XP from quests remains the same.