Here is photo below. I raised these myself, so there are no chemicals on them. Thanks in advance for your help.
What a cute garden! The salvia looks like mealycup sage. I didn't find it in any references for using herbs in bath teas, salts, or aromatherapy. Suggested plants were lavender, chamomile, rose, pepperment and rosemary, for example. You can consult an herbalist for a more definitive list.
https://www.gardeningknowhow.com/edible/herbs/hgen/medicinal-herb-plants.htm
I have read that salvia is a perennial and can be cut back for the winter. Is this true for winters in Massachusetts and if so what procedure do I use to cut.
There are some salvias hardy in zone 5 such as salvia azurea but there are lots more that are annuals or tender perennials. You would need to know what variety of salvia you have and look up its hardiness zone. Any salvia can be cut back in late summer for a new flush of blooms in fall.
https://www.gardeningknowhow.com/ornamental/flowers/salvia/growing-different-salvia-types.htm
I have grown both for the first time from plug plants. I need the space for winter flowers but am not sure if I should dig them up or leave them. Both have a large healthy root ball.
There are annual and perennial varieties of salvia so it depends on what variety you have.
Agastache is perennial in colder zones and most likely is perennial in your location. So I wouldn't pull it out.
https://www.gardeningknowhow.com/edible/herbs/hyssop/growing-agastache.htm
https://www.gardeningknowhow.com/ornamental/flowers/salvia/growing-different-salvia-types.htm
If so is consumption dangerous?
No, it isn't. It is Verbena bonariensis. All Salvia will have that typical "sage" smell. Once the plant is scratched, there will be no doubt that it is a sage. I would not eat it.
https://www.gardeningknowhow.com/ornamental/flowers/verbena/common-verbena-plant-varieties.htm
The bottom leaves all have little holes in them.
Here are some natural pesticides you can use:
https://www.gardeningknowhow.com/special/organic/what-are-organic-pesticides.htm
How to care for Salvia?
If you have a specific salvia, do a search for it on gardeningknowhow.com. Otherwise, here are general instructions:
https://www.gardeningknowhow.com/ornamental/flowers/salvia/growing-different-salvia-types.htm
Hye. I'm from Malaysia. As here we're in tropical climate, does salvia farinacea fit to be planted here?
Salvias do well in hot, dry conditions, so it should do well.
https://hgic.clemson.edu/factsheet/salvia/
https://www.gardeningknowhow.com/ornamental/flowers/salvia/blue-salvia-growing-conditions.htm