I've been working in almost exclusively audio with X3 and only recently added a midi controller which I still can't use effectively... but one problem I notice is that the projects I've created to work in the MIDI format seem to take forever to load up... my audio track projects load up normally... is this to be expected?

Projects with sample based synths like DimPro and Session Drummer may load slower because they must load all the samples used by the synth programs. Some programs can use 100's of MB.

Yeah the more synths and sample libraries you have, the longer the load time. I have some large MIDI heavy projects which take ages to load (and also freeze up my browser as they're loading). Of course you can reduce load times considerably by putting your sample libraries on an SSD.