the vermiculite content really depends on how you are watering and the rest of your mix.
since you are heavily using topsoil and compost they will already absorb quite a bit of water ( eventually will just be mud )
You don't need the extra water retention that vermiculite gives you. it just another extra thing to buy that isn't doing much for you.
it doesn't hurt really though, unless you are in a super wet area and the mix ends up holding too much water, the chunks should not compact as much as your mud so helps give the soil some body.
vermiculite is more useful in a mix that is too fast draining, like a heavy wood, rocky, or sandy mix.
but even then we can use other things to hold water. so it is not necessarily required.
peat is only hydrophobic when it is bone dry, it will take a long while for the peat to dry out in normalish sized containers ex 20L, 5gal, for smaller containers (like for baby plants) it will dry out faster.
in a very high peat mix (like 80% +) i can see it being useful as a kinda "oh shit" scenario.
but if you are mixing other things (ex compost) in your mix not just peat, its fine they will still hold water even if peat gets dry.
if you have a system to control your water (automatically or manually) and will be watering very often we don't need / want extra water retention.
example: watering thoroughly everyday will not give time for most mixes to dry out.
or extreme solutions like dutch buckets or self watering containers where water is always available we don't want the mix to hold extra moisture if we don't need it..
If you are doing infrequent watering or live in an area where you are relying on rainfall that is somewhat infrequent or very arid. then vermiculite will be great as will it help keep some moisture in your soilmix over the dry days.
so i'll just say that's my reasoning behind not using vermiculite.
others can disagree, you can use it, i won't judge, i just wouldn't use it.