The Science of Soils
One of the keys of successfully growing Lavender is, without a doubt, proper soils. These plants, regardless of type, despise wet root systems. Moisture at the crown/base of the plant is sure-fire way to kill your Lavender plants.
Soils with good drainage that will not hold water on the surface are best. This allows you to water them deeply but prevents water from resting around the top of the root structure. If you have heavy/clay soils, amend with some organic material before installing your Stone Cottage Farm plants.
If planting in a container, try to ensure that your potting mix is high in organic material and porous enough to drain properly. Since pots are inherently better draining that soil, you're already a step ahead. Just make sure that you water enough during the hot days of summer. Even though Lavender like it dry, you'd be shocked just how much water they'll use in 90-degree weather when they're pushing flowers!
Don't fool yourself into thinking that Lavender will do just fine in the shade. They need full sun for a multitude of reasons. Sunlight keeps the foliage dry - a key to keeping your Lavender happy and healthy. The sunlight also gives the plant the energy it's used to in it native habitat. If you can place it in a spot that gets good air circulation, even better.
These rules still apply when planting in containers - full sun and good air circulation are key to keeping the plant free from issues.
The only place where some dappled afternoon sun would suffice would be in areas where extreme summer heat occurs. With multiple days above 85 degrees, your Lavender plant could handle the light shade - providing there is ample air moving around the plants.
Don't Kill With Kindness
At the end of it all, Lavender are fairly low-care plants. Water deeply but not frequently. If you can irrigate in the morning and allow the plant to completely dry before nightfall, you'll help prevent any disease issues.
When it comes to fertilizer, they perform best in soils that are low in fertility. A little organic matter/compost each spring should suffice in storing whatever feed the plant needs. The only other amendment that could be suggested would lime - Lavender prefer soils that are pH between 7.0 and 8.0.
The only trimming that we could consider necessary is pruning the plant lightly after the new growth appears in spring. This will give you a fuller plant that will be less likely to flop under the weight of it summer flowers. Besides that, you can trim the tips off during flowering if you are harvesting them for drying. Regardless of when you trim, be sure to not cut into the old woody stems of the plant.