Sounds about right, I’ve used paving slabs before, set onto a dry mix of sand and a bit of cement. Ive then laid the deck beams onto the slabs, using spacers or fillets to fine tune the level/fall. Whether that’s correct or not, I don’t know, however, that deck is still there and doesn’t rock or twist some 6 years on!
If you go to collect your deck boards from Doug and Wink, they also have masses of off-cuts of varying lengths and sizes. I will often go through that pile for stuff suitable for deck beams and they’ll readily do a cash deal on those bits.
I like rustic and a rustic deck sounds like a fun project. Enjoy! 😀