I guess your harddrive is broken. Never heard about a hard drive size limit.

You cannot create a partition bigger than 127GB with MorphOS and SFS and there is a size limit for the HFS Boot Partition. Everythinig else should work. But I would not get some 320GB model as those are probably quite old and expensive. The 160GB Model I have in my mini was quiet expensive back then.

Since you need IDE I would go for some 2.5" mSATA interface (DeLock) and some mSATA SSD. Those are available in bigger sizes and even if you just go for 250GB the speed benefits are great.

[ Edited by geit 28.05.2016 - 21:09 ]