Hardscape / landscape- Suggestions, please!

Where are you located? How steep is the hill? Will you be physically capable of weeding the area?

If you had picture or even a sketch it would be easier to answer. But there is some advice I can give anyhow.

Roots!

The roots of the existing trees absolutely WILL interfere with work on the hill below. Damaging those roots can wind up causing severe damage to the trees. Also noteworthy is how much erosion control a root system will provide. A lot!

Some of the best erosion control measures are plantings. Talk to a good garden centre ( take along some pics) about what plants are suited to you area and your style with a good root system and consider planting rather than hardscape. Cheaper and the right plants can be virtually maintenance free after the first couple of establishing years.

Brick wall planters, these take 36 bricks and mortar per each planter you place at the base of a hill. And are 6 bricks @ 6 levels, if you stand those on their wide sides, and use enough mortar these should stand at least 24 inches high.

You then have a place to put the erosion, off the hill.

If you think those are not large enough, you can also use a 36 brick design that I usually recommend or include in plans for either: Firepits, Containing bushes & wildflowers, on patio Ice-Box, Benches and sidetables.

7 @ the base in a Septagon Shape

7 @ Level 2

6 @ level 3

5 @ level 4

4 @ Level 5

3 @ Level 6

2 @ Level 7

Again, a brick has 6 sides, and need not always place the depth side at the depth rather than the height.