हमने प्लान पर बहस की।

हमने is हम + ने.

The postposition ने is used with the subject of many completed transitive actions in Hindi. Since बहस की is a completed action in the past, standard Hindi uses ने:

• हमने बहस की = we debated / we argued
• not normally हम बहस की

So हमने means we as the doer of the action in this sentence.

It is in the perfective past.

That means the action is viewed as completed. In English, it is often translated with the simple past:

• हमने प्लान पर बहस की।
  We debated the plan. / We argued over the plan.

So this is not a habitual meaning like we debate and not a progressive meaning like we were debating.

With बहस करना, Hindi often uses पर to mean on, over, or about the topic of debate.

So:

• प्लान पर बहस करना = to debate the plan
• literally, something like to do debate on/over the plan

This is a very natural pattern in Hindi.

Yes, you could.

• प्लान पर बहस की sounds very natural and compact.
• प्लान ke baare mein बहस की is also understandable, and it makes the about idea more explicit.

In many contexts, पर is the more idiomatic choice with बहस करना.

In Hindi, nouns before postpositions usually go into the oblique case. But some nouns do not show a visible change in the singular.

प्लान is a consonant-ending borrowed noun, so its singular form stays the same:

• direct: प्लान
• oblique singular: प्लान

That is why you get:

• प्लान पर

Compare that with a noun like लड़का, which does change:

• लड़का
• लड़के पर

It is an English borrowing, and it is very common in modern Hindi speech.

So प्लान is completely natural in everyday Hindi. Depending on style, you could also use a more native/formal word such as:

• योजना

For example:

• हमने योजना पर बहस की।

That sounds more formal than प्लान.

Hindi very often forms verbs with a noun + करना pattern.

Here:

• बहस = debate, argument
• करना = to do

So:

• बहस करना = to debate, to argue

In the past perfective, करना changes form, giving:

• बहस की

This kind of structure is extremely common in Hindi:

• कोशिश की = made an effort / tried
• बात की = talked
• मदद की = helped

Because बहस is a feminine singular noun.

In this kind of noun + करना construction, the perfective form of करना often agrees with the noun part:

• बहस की because बहस is feminine
• कोशिश की because कोशिश is feminine
• काम किया because काम is masculine

So बहस की is the expected standard form.

Not exactly.

• बहस often suggests a debate, argument, or some disagreement
• चर्चा is more like discussion

So:

• हमने प्लान पर बहस की can sound a bit more argumentative or debate-like
• हमने प्लान पर चर्चा की sounds more neutral: we discussed the plan

Both are possible, but they are not identical in tone.

It is quite natural.

• हमने = standard past construction
• प्लान = very common everyday borrowing
• पर बहस की = natural collocation

So the sentence sounds normal in modern Hindi, especially in conversation or general informal use.

Yes, Hindi word order is somewhat flexible, though the given version is very natural:

• हमने प्लान पर बहस की।

You might also hear:

• प्लान पर हमने बहस की।
• हमने बहस प्लान पर की।

These alternatives can shift emphasis, but the original sentence is a straightforward neutral order.

A simple pronunciation guide is:

ham-ne plaan par bahas kee

A few notes:

• हमने = ham-ne
• प्लान = plaan with a long aa
• पर = par
• बहस = bahas
• की = kee

So the full sentence is:

ham-ne plaan par bahas kee