I keep lasius neoniger the US variant. I'll answer what I can.
1. How aggressive are they to humans/other ants
Lasius n. are tiny and gentle. They can't possibly bite you and run rather than attack in most cases. The workers are smaller than poppy seeds. Tiny little nice ants to humans.
They can however be [censored] if faced by only one or two other ants, even larger ones in their own territory. In ant on ant violence being small and numerous can be an advantage. They are so small that some larger ants can't even really target them. But they can get overwhelmed. I guess I'm saying they can hold their own.
2. How hard is it to keep them
They are some of the easier ants to keep.
3. What are the best products for them ( is A.C. ant tower okay for them)
I like underground citi's little enclosures for them. They are escape proof for lasius and you can see what's going on.
4. How fast do they grow from the founding
Only my Pogonomyrmex are faster growing.
5. Do they tolerate more than 1 Lasius Queen from the same colony
No. I do think some people have done experiments on this... ant it can work for a little bit... but then a queen gets assassinated and you don't want that kind of drama in your formicarium. It's depressing.
6. What should I look at for
7. What natural decorations should I use and how
If you give them dirt or sand they will build stuff ... but it can make a mess. Always consider how new materials will impact your ants.
8. Finally, what is their favourite diet (do they accept human food aka. meat)an
Part of the reason they are easy is they love many foods:
house flies (crushed)
flightless fruit flies (live, they will hunt them... or frozen)
cricket parts (only a huge colony could deal with a live cricket and I don't think it's a great idea)
cat food
sugar water
jam, jelly
flowers (they will drink nectar)
spiders
mealworms (cut up and or frozen)
they only thing they have rejected was a rolly polly (Pogonomyrmex were happy to eat it)