I'm definitely getting a much clearer sense of where your hesitation is coming from after your history with your other cats! You're just wanting to do what's best for them and trying to minimize your stress because in your experience stress can lead to some negative effects down the road. I would say that what happened with your previous cats isn't quite the norm. It's challenging to tell what cats will reach to each other in certain ways.
But, there's also good news- the vast majority of cats can (and yours almost definitely will) learn to at the very least cohabitate peacefully. To have realistic expectations with cat introductions that is our goal versus them being friends. Not only does it seem yours will be fine with the time they need to adjust to each other, but if you DO start to see signs of territory or resource guarding (which is what it sounds like was going on with your previous cats) you now know what to look for and there's almost always adjustments you can make to the environment to help things become peaceful again. Your cats aren't showing that they want to be at each other's throats in a knock down drag out only one cat cat remain kind of way so this isn't going to be a worst case scenario of two cats that won't ever get along.
That's not to say they will never get in fights. Even cats that are friendly with each other may get into the occasional minor tiff. You can almost 100% expect there to be at least some swatting once they are together face to face. It's what comes next that's what you'll want to focus on. You can even see in one of my pictures in my current intro thread my NC swatting one of my RCs upside the head. What happened next was initially RC backing off, but then he was too focused on wanting to check her empty food bowl for residual flavor and she was determined for him to stay out of her room so that's where I knew the distraction had to come in and close the door. You'll get better at learning their body language and at doing a little mind reading as you go and there will be mistakes and dustups but that's OK. Sometimes even what feels like a backside ends up being progress because the cats may want to avoid it happenening again as much as you do!
But, there's also good news- the vast majority of cats can (and yours almost definitely will) learn to at the very least cohabitate peacefully. To have realistic expectations with cat introductions that is our goal versus them being friends. Not only does it seem yours will be fine with the time they need to adjust to each other, but if you DO start to see signs of territory or resource guarding (which is what it sounds like was going on with your previous cats) you now know what to look for and there's almost always adjustments you can make to the environment to help things become peaceful again. Your cats aren't showing that they want to be at each other's throats in a knock down drag out only one cat cat remain kind of way so this isn't going to be a worst case scenario of two cats that won't ever get along.
That's not to say they will never get in fights. Even cats that are friendly with each other may get into the occasional minor tiff. You can almost 100% expect there to be at least some swatting once they are together face to face. It's what comes next that's what you'll want to focus on. You can even see in one of my pictures in my current intro thread my NC swatting one of my RCs upside the head. What happened next was initially RC backing off, but then he was too focused on wanting to check her empty food bowl for residual flavor and she was determined for him to stay out of her room so that's where I knew the distraction had to come in and close the door. You'll get better at learning their body language and at doing a little mind reading as you go and there will be mistakes and dustups but that's OK. Sometimes even what feels like a backside ends up being progress because the cats may want to avoid it happenening again as much as you do!