If my partner and I take the next big step of living together, we would be bringing together two sets of pets (still an if at this stage, although we've both wondered how we would deal with all the pets if we did).

He lives on a 5 acre property with a big, gorgeous, cat friendly Rottweiller (Charlie) and a cat (Phoebe) that's adjusted to an owner who doesn't really like cats all that much, so doesn't get a lot of cuddles (unless I'm there). She's fairly independent, having gotten use to fending for herself when she has to. She'll often curl up with Charlie for a sleep, so they're totally use to each other. And a recent new addition (2 weeks ago) of his daughter's one year old cat (Wesley). Wesley hid in his daughter's room for almost two weeks because she wasn't around to help him settle in... so he's still quite nervous and Phoebe is still hissing at him. Then there are our two cats, Bow and Arrow, who have grown up in a suburban home on a piece of land that's perfect for cats.

If my partner and I did move in together we would build our own home and live on a few acres.

I can see Bow finding a warm spot on the verandah, watching us and the world go by. He might be okay with Charlie... I'm really not sure. I had noticed he found it difficult to breath on occasions when we had a house full of kittens - most likely because he was feeling anxious. We kept him in the loop (he was sitting outside the bedroom door when the kittens were born)... although he was definitely withdrawn during the time the kittens were around. He noticeably relaxed when Arrow was spayed and is back to being his usual aloof/cuddly self. Arrow is strong and independent, warm and loving all at the same time. She might find it easiest to settle in... although she could go a little feral if she wasn't watched.

My partner thought about a cat run... but then he's really a softy and wouldn't really like that idea. He didn't like the fact the bird life had pretty much disappeared around his house when there was just Phoebe... with four cats. Any ideas on how to potentially bring these animals together and keep them all happy & healthy?

A cat run or enclosure is not an entirely far-fetched idea, especially if you are building and designing your house. That way you could integrate it into the over-all plan. Think solarium or greenhouse, screened porch, outdoor living area, that sort of thing. The main idea may be for the cats to have a safe outdoor place, but that doesn't mean you can't put in a bench or hammock, etc. and enjoy being out there with them. The site below has some pictures and links to other cat enclosures, so you can get an idea of your options.

CatStuff: Cat Run

Thanks. I'm finding it difficult to picture any of these cats being kept in a cat run. However, it might be the only choice. A largish space with a cat door to the house could possibly work... and we could let them out occasionally while we're around.

I'm still wondering how the different personalities would interract and if there would be any vying for top-cat position. Bow Vs Phoebe (Bow's so soft and sweet... not a real fighter, but he has definitely taken on the role of protector at our place and being male, might naturally slot into the top cat role). Phoebe Vs Arrow (don't know who'd win that one - Arrow would probably be fine no matter what... they would probably put up with each other)... Wesley might never come out from under the bed...

Lots of vertical space will help. Female cats are generally more territorial than males, especially a female with kittens, so you may be surprised by who winds up on top. Read up on introducing cats, and take it slow. It might be good if you could design your house with two zones, since you are combining families and not just bringing in one new cat. That way, if worse comes to worse, you could have each set of cats with their own zone to live in. An advantage in your situation is that this will be new territory for both sets of pets, so they will all be looking to see how they fit into the new environment, instead of having residents that have already laid claim to certain spots.

Depending how cat-centric you are, you might want to follow the path that this couple did:
SignOnSanDiego.com > News > Features -- House for Cats

That's the famous "cat house" in San Diego. It includes 140 feet of cat walks, holes through walls, stairs, climbing columns, etc. All to make life nicer for 22 cats!