This is a bit of a ramble but I thought I'd cover it all....
Conditions wise, I think most species can be kept together if you are logical about it. A snail that loves warmth may not do well with a snail that can tolerate colder temperatures but the reverse is usually fine. Most African snails love warmth, even ones that can tolerate cold so you can't go wrong there. What I'm saying is that temperature-wise if your margie is happy, your others will be.
For humdity, you'll just have to just play it by ear. If your non-fulica are inactive and increased humidity makes them happy, keep an eye on your fulica. If there behavior changes for the worse then perhaps the conditions can't be balanced for the two. But I think they can. Margies love humidity so the bar is set by them really but I've seen pictures of fulica and margies kept perfectly ok together.
In most cases, you'll be fine. Good conditions are usually accepted by most species. I think the danger for fulica is that they will not be able to tolerate bad conditions for as long as some of the other snails. So in a tank with no ventilation that was way too wet, they'd be the first to die. Although I have no experience of this.
Luckily, snails react to environmental changes so usually you have time to react. Try a range of slightly different things, to find out what pleases them.
There are some minor problems with mixing snails:
They may crossbreed. That is not bad in itself as far as we know, probably quite the oppostite compared to inbreeding but it is usually undesirable. We have such a hard time with (mis)-identification it just confuses the matter. I mix snails I don't ever wish to breed, ones that are kept by lots of people.
Even if they don't crossbreed, you can't tell which species laid eggs unless you witness it. You may wish to hatch rarer snail eggs only to discover they are fulica and no-one wants the babies.
Certain species may be unsuitable. Margies for instance decimated wild populations of Arch. bicarinata because they carried a disease that they were tolerant of but the bicarinata were not. So there is a risk of species or breeding specific illness. In captive-bred snails, especially babies that probably won't have come into contact with other snails, you'll be fine. I mention this only because I am currently suffering a problem caused by what I think is some sort of snail virus and if I had kept more smaller tanks and split them up it may have helped.
Certain species of snail are predatory so this is worth knowing.
It is probably wise to keep African and European snails apart but many people don't and have no problems.
I mix species, and the only problem I encountered was a little predation on a panthera shell by a reticulata or stuhlmanni (can't remember now). It was as if they didn't recognise it as a snail shell. But for most people this isn't an issue.
It is also worth keeping similar sized species togther and species with vast differences in size apart. Snails tend to hang off each other and it isn't nice witnessing a small snail with a huge one hanging off it or even more than one. Snails can supposedly hold 10 times there weight, but it always worries me. Also babies tend to rasp the shell of the adults, seeing them as walking calcium.
It seems to me that the three species you keep will be fine together although your margie may bulldozer your other species slightly, being so big and bulky. I find babies can always avoid them and it never seems to matter, probably because there isn't enough for the big ones to hold on to. It is the large snails of smaller species that can get get crawled all over. But although I've seen some precarious dangling, I've not had any problems, although now I sort roughly to size.
I actually do mix Archachatina with Achatina that I wish to breed on the principle that they won't cross-breed and I will instantly be able to tell who laid the eggs with them being so different. So for example, I keep my margies and tigers together, they love the same conditions and are similar sized.
Perhaps the best solution would be a tank for your margie and perhaps even a friend

, and one for your others. But if you are restricted to one tank for them all, I think they will be ok together.
I don't think this ever stops, new arrivals complicate everything. ;D
paul