plane or engine first
I agree with Greg. Although I bought my engine before I had a turbine airframe (got a good deal due to a manufacturer sale price at an event), I think that in this market it will be better to buy the airframe and then buy the engine when you have reached the construction stage at which it is necessary.
Technology and company viability change too quickly for these products. You don't want to get stuck with either obsolete technology or an engine for which you cannot get service.
When you are ready for the engine try to attend an event nearby and look for sale prices.
Good luck.
Antony