Laying terrace slabs and avoiding weed growth

Hello everyone!

I want to create a terrace with 40x60 slabs of the type "Pallas grassano."
This is a first for me, so I have a question: What is the ideal substructure for this? Gravel or grit? What size/grain size? How thick should the layer be?
I don't want to have to constantly pull weeds out of the joints later on; how can I best avoid this? A friend said that if I lay the slabs flush, plant growth could still develop in the cracks; he recommended grouting the slabs with mortar. That seems a bit complicated to me... How would you do it in my place?

We have no mortar between the slabs and weed/grass keeps growing in the cracks. But it's not really a problem, you just have to remove it every now and then. What stopped us from grouting was the fact that if a slab ever breaks/ doesn't look so nice anymore/ you want something different, you can replace the slabs more easily...

If the mortar is too much effort, then just leave it. Then lay the slabs edge to edge and occasionally pull out weeds.

That looks good when something green is peeking out. For me, there is no mortar between these stones either. That little bit of weed is not a big deal.

The weeds would bother me and I have grouted the joints. The base is gravel and good compaction is important. The grain size is 32 mm and I applied it at 10 cm. It is all stable, looks good, and there are no weeds.

The joints are not the problem, and if a slab breaks, it can also be easily replaced. I have already relaid the entire terrace and removed the old slabs. That went perfectly well. What bothers me is the weeds between the slabs.