Constructing box stairs

I'm working on an old weatherboard holiday house that is on gently sloping ground. A treated pine deck surrounds the house and I'd like to construct box stairs leading to the lawn, so you could sit on the stairs and take in the view.

I've had a look on the web and will likely create oblong boxes that stack (see example Stairs: Box Steps | DIY Deck Plans) and finish these with treated pine decking. I see there are a lot of variations in box stair sizing, are there standard measures of tread and rise for steps and how far can you go in extending these to sit on without making the stairs awkward to climb. I've also seen combos (but not on the web) where there are wide sitting steps with a standard stair set in the middle.

Also, how do I connect the stairs to the ground? There is a 5-10 degree sideways slope, and I wonder if I need to put the support frames on steel stirrups to avoid termites? Or are there other ways to fix to the soil?

I have had for the last 8 years 15 temporary steps (3mtr rise) constructed of treated pine sleeper “U” shapes made from 200 x 50 treated pine sleepers. 1200mm wide with 600mm “legs” 2 x 100mm construction screws in each side. The soil is your basic clay mixed with push out from the cut and fill of the house build. I laid the first U on levelled ground and then placed the next U at 400mm back, rinse and repeat. So I have a 400mm tread with a 200mm rise (6mtr distance with 3mtr fall) each step is resting on the previous by 200mm every third or so step I screwed a scrap of sleeper internally to hold them together. Backfill was clay and infill of roadbase for last 50mm to “finish” the step. After 8 years the treated pine sleepers show no real wear above ground.
I am now in the process of replacing this temporary set of steps with the permanent steps. I will be building in a similar style.
What i have found after 8 years.
treated pine sleepers are 200mm and as a “rise” are to tall for a step (google regs state 110mm - 190mm) note treads can be varied in length but a consistent rise is important. I will build the new ones with 140mm x 45mm treated pine “boxes” topped with 132 x 32 blackbutt decking this will still give me a rise of 140mm (FIL is 90 years old and made a comment that my 200mm steps were getting a bit high for him)
the treated pine inground shows some deterioration not significant but I will coat my boxes with tanking paint as a boost to the treated pine.
i will still place the first one on levelled ground and I will still keep about 200mm resting on the previous, more in some cases as I too will be a bit creative and have some steps sections double as a seat, my largest width will be 3mtrs and I plan to offset left and right 2mtr and 1.8mtr long boxes up the slope keeping an imaginary 1mtr path through the centre( left and right to gain access to the garden for weeding and the centre width for quick up and down access)

longwinded but hopefully helpful, cheers
p.s. A standard seat height is 450mm i am going to use 3 x 140mm for my seat areas(420mm)
treated pine is treated for termites, or to resist termite attack. So steel supports are not required but will add to resistance cheers again

Thanks for that. Interesting the current stairs are sleepers on cement bricks and my parents are in their mid 80's, so a rail needs to be included as its a bit of an incline, but I take your note on the rise for seniors. My parents got their 70's back stairs replaced with wider treads and a gentler leadup, so I might measure those for comparison. Mind you, by the time I work out the design and spec the materials list its time to go back home. Never enough time for distant renovations.

The formula for an easygoing staircase is 2x rise +1x tread (2r+t) = 585-625mm.

If you are doing extended treads the maximum riser you want is 190mm

My old builder father always said to start at 7" rise with an 11" tread. (180mm x 280mm)
Variations can be made from there, but that was always your starting point.
I have found it to be just right.

Hooroo