Coils, I was talking ignition coils, as they can fail at any time and with no warning. But, don't fret over them, I've had just one failure in almost 10 years of Z4 ownership. I just carry a spare in the boot now, along with the very basic tools (a 10mm socket) required to change one if another was to fail.
As for hotels, I did 25 days across 11 countries last summer and most hotels were around €50-60 a night, most were pretty decent too. I think the most I paid was €90 for a Best Western in Zagreb, city centres are more expensive, rural are more reasonable and for me are preferable.
I generally just ride (motorbike) or drive until I see somewhere I like, or if I feel that time is getting on I'll look at apps like Trip Advisor or Google Maps and see what's about. You'll probably be surprised by the amount there are about, and some stunning places and locations too.
Going in June works for you as well, as you'll be out of main season so lower rates and more availability.