Looking at moving Velocity points to Krisflyer to book Brisbane to Europe next year. Can I for instance book Brisbane -Singapore- Moscow -Stockholm and get a free stopover at Moscow and come home from any other city in Europe that Singapore airline services? For instance Munich or Rome? Trying to work out best value. Thanks 
If you book it as a single return award, yes you’ll get a free stopover of your choice (pending availability of flights).
If you book 2x one way redemptions you won’t receive the free stopover (I made this mistake earlier this year).
Yes you can open-jaw book what you want. My recommendation would be to do your planned BNE>SIN>MOW>ARN (A359-A359-A359 good choices). For the return leg you’ll want to avoid ROME as it has the old J product (depending on when your travel is planned it may not be updated by then). Try to find a route with the new A380 J product, or just go out of MUC to get the current 77W J product to SIN which is essentially the same as the A359 one you’ll experience on the way over.
I mad the assumption you’re booking business class… even though you didn’t mention it.