Belgium has much to offer. Besides the good beers, chocolate, fries, culture, parties, ... the kiting is pretty good for the only 60km of coast. It sits between the Netherlands (everyone knows lots of Dutch big air riders) and France (with closest known spot: Wissant). The coast line is straight, which has its advantage you can easily make downwinders. Additionally there is a tramline running along the entire coast, which makes public transport for the downwinders super easy. The downside are the limited directions of wind to kite: from SW to NE is kiteable. But when it’s off shore in Belgium it’s not much more then an hour (or 2 depending from where) drive to France (Wissant/Wimereux) or the Netherlands (Brouwersdam, Maasvlakte,..).

Kiting can be done all year long (deep winter can be too cold, but lately it’s rare that it still gets that cold). In Winter you need a thick wetsuit (5 or 6mm), gloves, boots,... In Summer a 3/2mm is perfect.
Strongest winds are usually in Autumn, Winter and Spring. The wind can really be a bit of everything (foiling weather to 35kn). Weekly big air sessions are definitely possible, with periods of entire weeks of wind 20 knots. Now and then there are also some storms peaking at 45/50 knots. Looking at temperature and wind best months are: Sept/Oct/Nov/Dec and Mar/Apr/May/Jun. However in Jan and Feb you could have the biggest storms of the year.
In summer there is usually less (big air) wind. You’ll more need a bigger kite (12m) or go for foiling. Although 9 or 10m weather is definitely possible and usually we get a couple of storms passing by giving some nice 25-35 knots.
If there’s no wind you can chill at the beach, go for a sup, wake, kayak, ..., go visit inland cultural cities (Brugge, Gent, Brussel,...) or go to cities that has it all: culture, food, parties all night long (Gent, Brussel, Antwerpen, ...).