I agree that it is too tight. Have 2h margin I'd say.
Please note that you need to add to book Eurostar ASAP, even more if you need to take a specific train. There is a quota for passholders and it can sell out weeks in advance, especially between London and Paris. 30€ seat reservation
Check availability here : https://www.b-europe.com/EN/Booking/Pass#TravelWish
Let us know if you need alternatives and we'll gladly help.
Night trains are very popular so book them ASAP if you'd like to take them.
ICE trains from Belgium have optional reservations but are very popular so if you don't make one (3€ through ÖBB), you'll surely have to stand.