I grew up in one of the hottest driest places in Australia. My mother still lives in this place... Adelaide, South Australia and she lives in a house on a quarter acre, surrounded by a large garden with no lawn. Most of her garden is watered by drip irrigation.
Two elements are essential for success.
- Adequate water to sustain plants during periods of dry weather, delivered over a period of time; and
- mulch across the top of the soil.
There are pros and cons for placing the watering mechanism both over the top of or under the mulch.
Pros and cons for placing drippers under the mulch
Pros: greater water absorption, less evaporation, less likelihood of physical damage,
Cons: difficult to inspect and maintain, can become clogged from soil and other material becoming embedded in dripper outlets.
Pros and cons for placing drippers over / on top of the mulch
Pros: easy to inspect and maintain, unlikely to become clogged from soil and other material.
Cons: slightly less water absorption, slightly greater moisture evaporation (both of which can be alleviated by watering in late evening), greater likelihood of physical damage.
The type and number of drippers required is dependent on a few factors, that include:
- type of soil, specifically how well it both absorbs and retains water;
- profile of soil, specifically how deep is the topsoil and what type/s of earth lie beneath;
- availability to source of reasonably priced water;
In my mother's situation, small plants are watered by one single point dripper unit and larger plants and trees are watered by two single point dripper units. The lines are active for about two hours and the drippers / emitters run at 3-6 litres per hour, depending on type. While this doesn't allow adequate water for plants to flourish, it is adequate for survival which in that environment during summer is far more important.
Of all the different options you've mentioned in your post, it's worth noting that time and money are usually also a consideration for most people.
Not just the time and money to set the system up but also to maintain it over the years of operation.
So hopefully this summary assists. If you need any clarification add a comment and I'll update my answer.