Structured data (schema.org) for Price lists / service lists - schema.org

Question

I'm building a website for a local beauty salon. They offer services such as massages and various beauty treatments. It's all visible on 1 overview page (price list)
I found out https://schema.org/Product can be used for services:
Any offered product or service. For example: a pair of shoes; a concert ticket; the rental of a car; a haircut
Fist question, can I ignore fields like availability and condition?
Second, should I list this products as ItemOffered inside Offer? Or is this not the correct way?
Example:
{
"#context": "http://schema.org",
"#type": "WebPageElement",
"offers": {
"#type": "Offer",
"itemOffered": [
{
"#type": "Product",
"#id": "/beauty-treatment-a",
"description": "Short description with details",
"name": "Beauty Treatment A",
"offers": {
"#type": "Offer",
"price": "18.28",
"priceCurrency": "EUR",
"description": "Same description",
"name": "Same name",
"image": {
"#context": "http://schema.org",
"#type": "ImageObject",
"contentUrl": "image-a.jpg",
"description": "Same name",
"width": 640,
"height": 640
}
}
},
{
"#type": "Product",
"#id": "/beauty-treatment-b",
"description": "Short description with details",
"name": "Beauty Treatment B",
"offers": {
"#type": "Offer",
"price": "18.28",
"priceCurrency": "EUR",
"description": "Same description",
"name": "Same name",
"image": {
"#context": "http://schema.org",
"#type": "ImageObject",
"contentUrl": "image-b.jpg",
"description": "Same name",
"width": 640,
"height": 640
}
}
]
}
}

Answer 1

Fist question, can I ignore fields like availability and condition?
Schema.org never requires a property. A consumer, like Google, might require properties for one of their features.
For Google’s Product feature,
availability is recommended for the rich result in Google Search, and required for the "Related Items" in Google Images, and
itemCondition is neither recommended nor required.
However, their feature is only for pages about a single product. So your page is not eligible for Google’s Product rich result.
Second, should I list this products as ItemOffered inside Offer? Or is this not the correct way?
You can either have Product as top-level item (with offers Offer), or Offer as top-level item (with itemOffered Product).
About your example:
There is no need to use WebPageElement; it’s typically not relevant information that a certain HTML element on a page contains an offer, it’s only relevant that there is an offer.
You have one offer that consists of two products, and two offers that consist of one product each (the same like in the first offer). You probably don’t want to have the first offer (unless there really is an offer that combines the two products).
I would recommend the following:
Use OfferCatalog for the list of offers.
Each list item is an Offer.
Each Offer points to its Product/Service with itemOffered.