I never managed to learn Creole. It's an orally conceived and transmitted language, so if you do want to pick it up, that's really the way to do it. (The "specialists" are eternally divided over how to spell it, which makes learning it from books sth of a minefield.) You can live perfectly well w/o it, though. Your kids will pick some up at school, esp at primary level. I think that is the level where the diglossia is the most tricky.
I can find out about primary schools, and TBH that is one thing that I'd be looking into very, very carefully. I'm not overly optimistic about the quality of teaching on the island in the coming years, and the latest reforms to teacher training and University degree courses are not going to improve matters.
I'll need some geographical indications, though...is E. Salé temporary or are you likely to settle around there? Where will your DH be working? Are you going to be looking for work?
On that topic, it would probably be an excellent idea to go and see the place for yourself if you can. Just as there are numerous microclimates within a few km of one another, so the various towns/ areas are v different, and it's very much a question of personal choice. Unlike Frak, St Gilles/L'Hermitage, for instance, are not places I'd ever fancy living in. I never felt comfortable in the zoreyland atmosphere there - it's quite a bubble, the prices are sky-high because of it, and also TBH I don't find it the most attractive part of the island as regards landscape. And the heat is bad. Pre-kids, we never really went to the lagoon either, preferred Etang Salé, Grand Anse, etc. Boucan was our beach of choice when living in the North, but is not v kid-friendly.
One key factor is climate. A lot depends on how good you are in very hot, very sticky weather. Climate change is being felt in Reunion, and the last few summers have been very, very hot. TBH the weather is one thing I don't miss at all, I found it hard to cope with when working, driving, etc.
DH and I both hated the summer heat and humidity, and didn't want to live down near the shore. Summer is hard for pupils too, and the overhead fans in classrooms don't do much beyond stirring around the heavy, hot air. Unless you are OK with the idea of living in a place with air conditioning, which isn't sth I'd ever consider, you're better off a little higher up, about the ligne des 400 level, or a bit below it. You live and sleep better further inland.
Gardening is great. Around St Leu/St Gilles it's v dry, but elsewhere things grow like crazy. I once lazily chucked a passionfruit into a bougainvillea tree below the kitchen window as it had gone a bit bad, and within weeks a passionfruit vine had grown and it bore fruit that year. I'd have loved to have a lychee tree in my garden, we had friends who did and I have great memories of Christmas parties gorging on fresh lychees. Mangoes, too. Banana trees grow like nobody's business, and when you have a ripe bunch of bananas you have to give them away...
Don't know about Jardiland (you can look on pagesjaunes.fr), but there are several big garden cetres and lots of smaller ones. Orchids are fun to grow, too, and people are very into their gardens. If you are used to nice, soft, green lawns, though, you'll have to adapt, as the trainasse that passes for a lawn there is anything but.
Bizarrely, I had 3 phone calls and a letter from different friends in Reunion yesterday after posting on here! Have been feeling nostalgic, which explains my lengthy posts...