Personally, I would save up and get a decent set of filters.
I disagree that you do not need ND filters and strongly disagree that the 10 stop is all you need. I carry a 3,6 and 10 stop and the 10 stop is my least used filter because I don't much like that ugly, milky, flowing water look with no texture or detail. The 10 stop has it's place but is often used by lazy photographers to create what they like to call "fine art".
A CPL for landscape photography is a must IMO. Great for taking the glare out of windows, water or even leaves after rain. Improves contract and vibrancy. You can't replicate that in post.
I use Kase Revolution filters, the glass is strengthened and has a hydroscopic coating and I'm sure there are others out there that are decent. Cheap filters are usually cheap glass and have colour casts that can be difficult to remove.
ND grads can be replicated in post or by taking multiple exposures and blending them in post, BUT that's not always possible if you have moving things in your scene like the leaves and branches of a tree blowing in the wind. Good luck blending that. In such cases ND Grads can come in handy especially on older cameras with poor dynamic range.
I shoot with a R5 and haven't bothered carrying my ND Grads with me for a couple of years now because I can usually capture all of the data in one exposure. If I remember, you are learning on a 400D which will be a bit more challenging in those situations and I would say that if you start to see this to be an issue in your photography you'd be better off upgrading your camera rather than buying ND Grads. They can be expensive for a good set and you need filters, holders, step up/down rings etc.