I agree to a degree. Without more context it's difficult to say, but "Is this a porridge with meat?" makes it sound more ambiguous as if you are speaking about the type of porridge rather than a bowl of porridge that is currently present in front of the speaker. Typically, unless you're learning a new recipe for example, you would never refer to porridge with the indefinite article. The demonstrative pronoun "this" would indicate that it is understood to which porridge you are referring, generally the one nearest in physical proximity to you (the speaker). If referring to the porridge type conceptually, it would be most common to either include the word "type" or "style" if not using a different demonstrative pronoun like "that" to indicate its distance from the immediate.

you try it ;) I hate sweet porridge)

In this sentence, «це» and «ця» are really interchangeable. The difference is in grammatical structure:

• «Ця ка́ша з м’я́сом?» is analysed as [{is} {this porridge} {with meat}?] (i.e. ця modifies porridge),
• and «Це ка́ша з м’я́сом» is analysed as [is {this} {porridge with meat}?] (i.e. це is an independent pronoun).

Both are correct as the translation of the English sentence.

However, and in many sentences you can't use «це» and you only need to use «ця» (or «цей» for masculine nouns):

• Ця ка́ша вже захоло́нула. This porridge got cold already.
• Що ця люди́на собі́ ду́має?! What is this person thinking?! (собі́ makes this sentence more emphathic)