I would throw my opinion in with those who say avoid tartan ties. I have several tartan ties and wear them often... with trousers. Just not with the kilt.

Now, I know people who love to wear their tartan tie with their kilt, and even those who wear different ties of a different tartan than their kilt, and they think it looks just fine. So it is done. And probably no one will bat an eye if you choose to do it. However, my opinion, which is shared by many, is that non-tartan ties look better with the kilt. Solid ties are great. Club stripe, school or regimental ties look great with the kilt. Ties with small patterns in general look fine.

As to the question of wearing modern and ancient tartans together, sure this is certainly done.

The Atholl Highlanders are a prime example.