Se ni volas ŝpari, ni ne aĉetu tro da viando hodiaŭ.

Because aĉetu is the -u form, which is used for wishes, requests, suggestions, commands, and exhortations.

Here it means something like:

• let us not buy
• we should not buy

So Se ni volas ŝpari, ni ne aĉetu tro da viando hodiaŭ is not just stating a fact. It is making a suggestion or recommendation.

Compare:

• ni ne aĉetas = we are not buying / we do not buy
• ni ne aĉetos = we will not buy
• ni ne aĉetu = let us not buy / we should not buy

Yes. In Esperanto, the -u form can be used with all persons, including ni.

With ni, it often corresponds to English let's or let us:

• Ni iru. = Let's go.
• Ni manĝu. = Let's eat.
• Ni ne aĉetu tro da viando. = Let's not buy too much meat.

This is completely normal Esperanto.

In Esperanto, ne normally goes before the word it negates. So:

• ni ne aĉetu = let us not buy

Putting ne before the verb is the standard way to negate the whole action.

Because tro da is the normal pattern for saying too much of something or too many of something.

• tro da akvo = too much water
• tro da libroj = too many books
• tro da viando = too much meat

The word da is used after quantity expressions when you are talking about an amount of something.

So:

• tro da viando = an excessive amount of meat

Because viando here is being treated as an uncountable substance, like meat in English.

When Esperanto talks about an amount of a substance after da, it usually uses the singular form:

• multe da akvo
• iom da pano
• tro da viando

If you used the plural, it would suggest separate countable items or kinds, which is not the basic idea here.

Because viando is not the direct object of the verb by itself in the usual way here. It is part of the quantity expression tro da viando.

In Esperanto, after da, the following noun does not take -n just because the whole phrase is the object.

So:

• Mi trinkas multe da akvo.
• Ni ne aĉetu tro da viando.

The noun after da stays without -n.

Because the sentence is talking about a real present situation: if we want to save.

In Esperanto, se does not automatically require a special conditional form. You use the tense or mood that fits the meaning.

So:

• Se ni volas ŝpari = If we want to save
• Se ni volus ŝpari = If we wanted to save

The second one sounds more hypothetical or less direct. The original sentence is more straightforward and practical.

Ŝpari usually means to save, especially in the sense of:

• saving money
• being economical
• using less of something

In this sentence, it most naturally means to save money or to economize.

So Se ni volas ŝpari means something like:

• If we want to save money
• If we want to economize

It is normal and recommended here because the sentence begins with a subordinate clause:

• Se ni volas ŝpari, ...

That comma helps separate the if clause from the main clause. Esperanto punctuation is often fairly flexible, but this comma is standard and makes the sentence clearer.

Yes. That is a very natural way to understand it.

The -u form with ni often overlaps in meaning with English expressions such as:

• let us not...
• we should not...
• we shouldn't...

So depending on style, the sentence can feel like either:

• a suggestion to the group
• practical advice
• a mild exhortation

Yes, hodiaŭ is fairly flexible in position.

These are all possible, with slightly different emphasis:

• Se ni volas ŝpari, ni ne aĉetu tro da viando hodiaŭ.
• Se ni volas ŝpari, hodiaŭ ni ne aĉetu tro da viando.
• Se ni volas ŝpari, ni hodiaŭ ne aĉetu tro da viando.

Putting hodiaŭ at the end is very natural and keeps the sentence smooth. It adds the time information after the main idea.

Yes. If you remove it, you get:

• Ni ne aĉetu tro da viando hodiaŭ.

That still makes perfect sense: Let's not buy too much meat today.

The se clause just adds the reason or condition:

• If we want to save, let's not buy too much meat today.

So the first part frames the advice, while the second part is the actual suggestion.