People will be reluctant to give advice for stuff like this. It hard to do as every situation is different.
First off, code - Around here every little town is different. To know for sure any code issues you will need to contact your local code enforcement.
The rest of my comments are very general and may or may not apply to your situation.
When opening up a wall that is load bearing you will need a header and posts to carry the weight of whats above that was previously supported by the wall.
You may have other things that can be a challenge as well.
- matching up the floors
- re-routing of electrical
- re-routing of ducts
- re-routing of pipes
Lots can be involved or it can be relatively simple. Often the hardest part is fixing up the floors in the new space between the two rooms. This is easy if you are going to re-do one or both of the floors.
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