So when you said "In that case, and based on the numbers you provided, daily partitioning seems a decent solution."
, does it mean that size of the partition (which will be ~100-150GB per partition here) is not an issue for the postgres to serve read latency sensitive queries?
Yes, that should be fine. At the end of the day, what's going to be more important is making sure you are using good indexing, and keeping all your active stuff in cache. Since you have 127 columns, only pull back the columns you absolutely need for each query.