Engine oil Mannol or IDEMITSU

OP I have the same car and engine as you, I've been using the cheap Mannol stuff, whichever is cheapest. Also whichever the cheapest oil filter is from ECP at the time. Car is currently on 120k and I've been doing this for at least 5 years and it hasn't eaten itself yet!

You can actually get decent quality oil which is not from an expensive brand for pretty cheap, particularly if you buy a 20l jug.

For example, Mannol offer fully synthetic oils which meet OEM specifications

Been using Mannol 5w30 Full Synthetic for past 35k miles now without any issues.

For the UK, cheap and good: Mannol Fully Bi-Synthetic Engine Oil Longlife 3 5w30

The car runs well, no problems starting up, no significant oil burning.

I use Mannol 7715 on my 3.0tdi

I think Idemitsu is the better option if you have access to it. Mostly because it was developed for the rotary engine.

I use the mannol 5w30, it might be cheap but it's still just as slippy

Idemitsu to both, because it’s designed and tested on rotaries.

I use idemitsu rotary 20w50

Personally I use 5w-30 because it's the cheapest. I've used 0w-20 and 0w-30 in the car also. Can't tell what is in the car at any given time as it runs exactly the same regardless so just use the cheapest that's still up to the relevant specifications.