Gravel vacuuming a planted substrate is not necessary, especially in the first 6 months. But you can certainly do so if you find a lot of muck in the substrate. If you have lots of root plants, then vac less. If you have very little rooted plants, like mosses and ferns with roots above the substrate, then vac more - even then it's not necessary to vac very often.
I use a glass feeding dish to minimise food falling in between the substrate, that helps minimise the need to vacuum. You should try a feeding dish as well.
When you find your water parameters like TDS, and GH climbing and water changes are not helping to bring it down to CRS/CBS suitable levels ... then a substrate vac might be in order. For the most part, just a simple water change is all that is required.
1.5 inches is ok for most tanks. But since you have a 2.5gal tank, start at 1inch.
The substrate will be rich when new, and can/could cause the pH, to drop too much in such a small tank.