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Have I used the present continuous and future simple (going to) tenses correctly below?

We are heading to Paris tomorrow by train. We are spending the day there and are back in London for the night before (we are) going back to New York on Saturday morning. From there we are taking a flight to buffalo to see niagara falls, which is on the border of Canada and USA. We are going to see it from the Canadian side. After that, we are going to Toronto and are spending a few days there before (we are) going back to LA and then back home.

Is it possible to use the two tenses interchangeably in any of the sentences in my paragraph? If yes, which one/s?

Thank you.
Comments  
Future continuous can't be used anywhere in the paragraph, right?

"It describes the idea that an action will happen in the normal course of events. It refers to routine activities, not intentions, decisions or plans."

eg- We'll be going overseas next weekend - Incorrect since it's a plan and it's not in the normal course of events?

We are going overseas next weekend.
I am combining your questions.
hammerman1We'll be going overseas next weekend - Incorrect since it's a plan and it's not in the normal course of events? Yes, it is absolutely correct.
We'll be going overseas next weekend
We are going overseas next weekend
Core meaning is the same between the two. The present progress future is better used for contexts with conceptually near future. For remote future, "will" is still a better choice.

Your narration of the itinerary in the first post is easily understood. However, a few spots perhaps should be better expressed by simple future, rather than present progress future, in my opinion. I lighted them in red.

We are heading to Paris tomorrow by train. We are spending the day there [ok] and are back in London for the night before (we are) going back to New York on Saturday morning. From there, we are taking a flight to buffalo to see niagara falls, which is [at] on the border of Canada and USA. We are going to see it from the Canadian side. After that, we are going to Toronto [to spend] and are spending a few days there before (we are) going back to LA and then back home.
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We are heading to Paris tomorrow by train. We are spending the day there and are back in London for the night before (we are) going back to New York on Saturday morning. From there we are taking a flight to Buffalo to see Niagara falls, which is on the border of Canada and USA. We are going to see it from the Canadian side. After that, we are going to Toronto and are spending a few days there before (we are) going back to LA and then back home.
____________________________

before going back / before we go back. Not before we are going back.

We [head / are heading / are going to head / are going to be heading / will be heading] to Paris tomorrow by train.

We [spend / are spending / are going to spend / are going to be spending / will be spending] the day there and [will be / are] back in London for the night before [going / we go] back to New York on Saturday morning.

From there we [take / are taking / are going to take / are going to be taking / will be taking] a flight to Buffalo to see Niagara falls, which is on the border of Canada and USA.

We [are seeing / are going to see / are going to be seeing / will be seeing] it from the Canadian side.

After that, we [go / are going / are going to go / are going to be going / will be going] to Toronto and [spend / are spending / are going to spend / are going to be spending / will be spending]a few days there before [going / we go] backto LA and then back home.

Many of the tenses you are working with can be used interchangeably.

CJ
hammerman1"It describes the idea that an action will happen in the normal course of events. It refers to routine activities, not intentions, decisions or plans."
I don't agree with this characterization of the future continuous.
hammerman1We'll be going overseas next weekend - Incorrect since it's a plan and it's not in the normal course of events?
Again, I don't agree. There well may be a context in which this turn of phrase is exactly what you need.

CJ
CalifJimWe are heading to Paris tomorrow by train. We are spending the day there and are back in London for the night before (we are) going back to New York on Saturday morning. From there we are taking a flight to Buffalo to see Niagara falls, which is on the border of Canada and USA. We are going to see it from the Canadian side. After that, we are going to Toronto and are spending a few days there before (we are) going back to LA and then back home.____________________________before going back / before we go back. Not before we are going back.We [head / are heading / are going to head / are going to be heading / will be heading] to Paris tomorrow by train. We [spend / are spending / are going to spend / are going to be spending / will be spending] the day there and [will be / are] back in London for the night before [going / we go] back to New York on Saturday morning.From there we [take / are taking / are going to take / are going to be taking / will be taking] a flight to Buffalo to see Niagara falls, which is on the border of Canada and USA.We [are seeing / are going to see / are going to be seeing / will be seeing] it from the Canadian side.After that, we [go / are going / are going to go / are going to be going / will be going] to Toronto and [spend / are spending / are going to spend / are going to be spending / will be spending]a few days there before [going / we go] backto LA and then back home.Many of the tenses you are working with can be used interchangeably.CJ
Thanks CalifJim and dimsumexpress.

Given that everything is already arranged (plane tickets, train tickets etc), is it still ok to use any of the 4 alternatives?

one eg- Tomorrow, I'll be catching / I'll catch a flight to london, and then I'm spending three days there to visit the historic attractions.
(The first half the sentence is already arranged, while the 2nd half isn't, but a more definite tense is being used in the 2nd half of the sentence.)
Is the sentence ok regardless of what I've put in the brackets?
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Tomorrow, I'll be catching / I'll catch a flight to London, and then I'm spending three days there to visit the historic attractions.

The simple future is not as likely to be used there, though it's not wrong. I would use one of these.

Tomorrow I'll be catching a flight to London, and then I'll be spending three days ....
Tomorrow I catch a flight to London, and then I spend three days ....
Tomorrow I'm catching a flight to London, and then I'm spending three days ....

CJ