Looking at your previous posts you are trying to use collective.exportimport.
I agree: that's the way to go!
But you might have some surprises depending on some very specific quirks of your installation that are impossible to predict without first assessing your installation.
You might find out that, for example, that it requires too much RAM to to export all your content at once.
Or that it might take an unacceptable amount of time to do the import.
If that happens you might need to face hard problems to solve.
You can just try do simulate the migration, post your troubles here and see what happens.
As @zopyx mentions, the more internal code you have the trickier it can get, you can try to use collective.exportimport to export only a few selected content types and see how the migration goes on the new plone site, and build from there.
Some interesting numbers to get an estimate would be:
how many content types you have?
how many objects on the database exists?
how many custom distributions you have?
Depending on the size, it is feasible to already work with a complete export of the website, but if the amount of data is big, trying a partial migration to build trust on your approach might be best
Fortunately you are at the right place, the plone community, where we can give you some help, but if the problem feels too much, you can always contact any of the companies that work on Plone on a daily basis to get a quote from them. See a list of providers.
Does your company have some budget for the migration?