Over half of secondaries are Catholic. Religious instruction is obligatory for 2 hours throughout secondary, at a Catholic school it means only Catholic religious instruction, at a communal, provincial, French Community funded, non religious aligned school, there is always a choice of religious instruction eg Catholic, Protestant, Morality, Judaism. It's a generalism to say the majority of academic secondaries are Catholic, there are a minority of non Catholic schools are too. I'm guessing looking at Notre Dame's options it's an academically strong school.
For the first 2 years of secondary, all children in French schools study 4 hours of a modern language. In some schools in Wallonia, there is no choice and it's Dutch, in other schools there is a choice of English too. You can only add another modern language from 3rd secondary.
Schools which offer English in 1st/2nd secondary :
AR Maurice Careme Wavre - also does English immersion
College Technique St Jean Wavre
Institut de la Providence Wavre
Institut Provincial Wavre
Le Verseau - Wavre (Bierge)
Lycee Martin V - LLN
Only Notre Dame de Basse Wavre and Institut St Jean don't do English from 1st secondary. I noticed these schools also appear to offer the most academic options ie Latin and no "professional" or "technical" streams, include Lycee Martin V in that too actually. From that I can only guess these are the 2 most academic schools in the area. But ask the parents of children at your primaire if this assumption is correct.
You're right, only Martin V starts Spanish in 3rd, other schools don't include it until 5th.
You would have to think about the fact that, with the exception of Le Verseau, English will be taught as a foreign language and how much exactly will an anglophone child find this useful? From the point of view of confidence, it could be quite a boost as your child should be top of the class. However, just how stimulating will it be? Same goes for Spanish. The curriculum by 3rd consists of around 32 periods a week, if 8 periods are spent (4 English and 4 Spanish), that's a third of the week, studying languages aimed at those learning the language and not at those who speak it as mother tongue, you have to think about whether this is not "wasted" time or whether the school could cope with a child who knows it better than the teacher, which is going to be pretty likely, Le Verseau excepted.
Finally, the biggest disadvantage of LLN I can see is that Wavre is a 20-30 minute bus ride away, whereas LLN requires a change of bus in Wavre and is 1 hour by bus away and will mean leaving for school perhaps before 7am. It's fine if there is a non working parent who can get there and back, but there are after school activities too, is this practical to have this distance between school and home? Sorry just my own preferences intruding here, we have the luxury of son's secondary school being a 15 minute bus ride away and all his after school activities he can get to himself, which he has to do as both of us work.
Oh another thought, you would really have to seek advice of primaire whether children have made it into Lycee Martin V from your primaire in the last 2 years without priority, as you will be choosing a school NOT of the nearest type to your house and primaire and you may get quite low points which will lower the chance of getting in to Martin V from where you live. If Martin V is oversubscribed, the higher the points the better. If you don't get your first choice, it's often a case of not getting your 2nd 3rd 4th choices too and having to wait until August to get one of the remaining places. I don't know how oversubscribed schools are in your area are though, it may be that there are always places in all the Wavre - LLN schools.