Don't give up hope. Moder is a fairly easy fight if you prepare a strategy so that any random mobs don't interfere with the actual boss fight.

The plains however can be challenging until you get a decent farm going for better food and barley wine. But if you have a lot of poison arrows and can snipe from a good distance it's doable, you just have to portal out from time to time if you pull too much.

Yagluth fight is a case of recognising his animations and hiding when necessary, in basic terms it's a lot like the second boss fight only more brutal. Again you need a strategy to stop additional mobs getting involved. There's even a very long winded strategy to stop deathsquito's interfering, involving a stakewall with additional bits added to the wall. Firespark on YT developed it to stop deathsquitos getting him during farming.

Took me over 500 hours to reach the Mistlands solo, though I do spend a fair amount of time building stuff and many deaths, so long as you keep your bow skill and weapons of choice around 50 you should be ok. Mistlands you going to want running and jumping around 50 too.