In the following sentence:
发言人表示，该公司目前为多达80款不同菜系提供外卖，“这一点足以说明我们英国人是全世界菜肴的吃货。”
I understand the meaning, which is something like the follows:
The spokesman said that the company now provides 80 different types of delivery foods. This is more than an enough explanation of why British people are the best gourmet in the world.
However, what does the 为 mean in this sentence? I feel that the subject is 该公司 and the verb is 提供外卖, so 为 would be a preposition...
Does it mean "with" or something others?
You almost get it.
为...提供 means "provide ... with" or "supply ...with"
Hence, the correct pronunciation here is wei4, not wei2.
Depending on the verb, 为, as a preposition, can mean "for, to, with". Prepositions in English and Chinese are quite different I think.
该公司目前为多达80款不同菜系提供外卖
Here we can extract the stem of the sentence: 该公司目前提供外卖. So 为多达80款不同菜系 is an introductory phrase. "为" here means "facing to"baidu.
该公司目前为多达80款不同菜系提供外卖
This sentence is grammatical, but illogical. 为 菜系 提供 外卖, you can not provide 外卖 to 菜系， but you can only provide 外卖 to 人.
The sentence could be paraphrased as:
该公司目前有多达80款不同菜系（可）提供外卖
Your translation is mostly right, although the original sentence would be the closest to:
The spokesman said that this company now provides delivery services for as many as 80 different food types, [...]
and 为 in this context means "for". What makes it not that obvious at first glance is because this sentence in Chinese is not structured the same way an English speaker would naturally construct it. It literally looks a bit like this:
[The spokesman said], [this company] [now] [for as many as 80 different food types] [provides delivery services], [...]
It's now much easier to see that 为 is the preposition that actually introduces the coordinate clause of the sentence, indicating the target for which the company provides service.
In fact, if you look the word up in the dictionary (or just Google it), you can find "for" as one of the main definitions for this word. Hope that helps.
发言人表示，该公司目前为多达80款不同菜系提供外卖（服务），“这一点足以说明我们英国人是全世界菜肴的吃货。
Without context it is always a bit dodgy interpreting. That said, it is extremely unlikely that any one kitchen would prepare and provide more than 80 different cuisines. Therefore, the company in question is a delivery service like 饿了吗. They provide their service for the dishes, so I think '为多达80款不同菜系提供外卖（服务）' is not illogical.
However, to describe the British as gourmets is not just illogical, it is counter-factual! ("I'm hungry, help me open this can of baked beans!")
为多达80款不同菜系提供外卖（服务） we provide takeaway service for more than 80 different cuisines
