Раз уж так, то давай спокойно обсудим это вечером.

Раз уж так is a fixed conversational expression meaning something like:

• if that is the case
• since things are like that
• well, if so

Here:

• раз can mean since or if that's so in colloquial Russian
• уж adds emphasis, giving the phrase a sense like well then or given that

So раз уж так sounds natural and idiomatic, not like a word-for-word logical construction. It often introduces a conclusion or next step based on what has just been said.

In Раз уж так, то давай..., the word то helps mark the result or conclusion:

• Раз уж так = if that is the case
• то давай... = then let's...

It is similar to then in English, but in Russian it is often optional in this kind of sentence. Including it makes the structure feel clearer and slightly more complete.

So:

• Раз уж так, давай... = possible
• Раз уж так, то давай... = also possible, and very natural

Давай + first person plural future/perfective form is a very common way to say let's do something in Russian.

So:

• давай обсудим = let's discuss
• literally, it is built with давай plus the form обсудим

A direct imperative like обсуди means discuss it! and is addressed to one person only. That would sound like a command, not a suggestion involving both people.

Compare:

• Обсуди это вечером. = Discuss it in the evening.
• Давай обсудим это вечером. = Let's discuss it in the evening.

Обсудим is the first person plural future form of the perfective verb обсудить.

In this construction, after давай, Russian uses this form to express let's do X:

• давай поговорим = let's talk
• давай решим = let's decide
• давай обсудим = let's discuss

Even though the form is technically future, with давай it does not mean simple future time by itself. It functions as a proposal.

Russian often uses the perfective verb after давай when the speaker suggests doing something as a complete action.

• обсудить = to discuss something through, to have the discussion
• обсуждать = to be discussing, to discuss in an ongoing or repeated way

In this sentence, the speaker means let's have that discussion and deal with it, so обсудим is natural.

If you used the imperfective, it would sound different and less standard here:

• давай обсуждать = let's start discussing / let's be discussing

That can work in some contexts, but давай обсудим это вечером is the normal way to say let's discuss it this evening.

Here спокойно most likely means calmly, without stress, or in a relaxed way.

So the idea is:

• let's discuss it calmly
• let's talk it over without getting upset
• let's discuss it peacefully

Depending on context, спокойно can also mean quietly, but in this sentence the emotional meaning is more likely: the speaker wants a composed, non-dramatic discussion.

Это means this or it, depending on context. In this sentence it refers to something already known from the conversation.

Russian often uses это where English might say:

• it
• this
• the matter
• the situation

So обсудим это simply means let's discuss it / this. The exact reference comes from context, not from the grammar of the sentence itself.

Вечером is the instrumental form of вечер, and Russian often uses this form to express time when something happens:

• утром = in the morning
• днём = in the daytime
• вечером = in the evening
• ночью = at night

So вечером does not mean with the evening here. It is just the normal adverbial time expression meaning in the evening / tonight in the evening.

It is informal to neutral-conversational.

Reasons:

• давай is informal and usually used with someone you speak to as ты
• раз уж так is conversational
• the whole sentence sounds natural in everyday speech

If you wanted a more formal version, especially with вы, you might say something like:

• Раз так, давайте спокойно обсудим это вечером.

That would be more suitable when addressing several people or one person formally.

Yes. Russian does not need to state the subject explicitly here.

In давай обсудим, the meaning is let us discuss or let's discuss, so the implied participants are:

• you and I
• or sometimes we more generally, depending on context

Russian often leaves subjects out when they are clear from the verb form or construction.

Yes, Russian word order is flexible, but different orders can change emphasis.

The original:

• Раз уж так, то давай спокойно обсудим это вечером.

This is natural and balanced.

Possible variations:

• Раз уж так, давай это спокойно обсудим вечером.
• Давай вечером спокойно обсудим это.
• Это давай спокойно обсудим вечером.

These are all possible in the right context, but the original sounds especially natural as a smooth suggestion. Russian word order often depends on what is already known and what the speaker wants to emphasize.

The tone is generally:

• practical
• calming
• slightly conciliatory

It suggests: since this is how things are, let's not argue now; let's discuss it calmly this evening.

So it is not just a neutral plan. It often carries a sense of trying to lower tension and move the conversation into a calmer setting.