Use of numbers in descriptions

Question

So far I've only learned how to use numbers in the context of counting e.g. このピザは 5枚ある (this pizza has five slices).

How do I express it in the following way:

This is a five-slice pizza

I would naively guess at "これは5枚のピザがある”, but I've not seen a counter used to modify a noun like that before.

Secondly, kind-of in the reverse direction how would I express the part in bold below:

(Please exit from) the front five coaches of this ten coach train

Hmm, I tried to construct this sentence but it just made me more sure that my guess for the first part of the question was wrong.

Answer 1

(Though I don't know if this answers your question:)

This is a five-slice pizza.

You normally say it as:

これは、５枚[切]{ぎ}りのピザです。
or
このピザは、５枚切りです。

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(Please exit from) the front five coaches of this ten coach train.

I think you'd normally say it as:

１０[両]{りょう}[編成]{へんせい}の電車の[前]{まえ}５両 / 前の５両 (から降りてください。/ 下車してください。/ お降りください。)