You can make cat fortress now. Or at least Crazy Cat Lady Fortress.
Send in your 7 dwarves as usual, except sell off an axe or two (you should get more than enough wood from the wagons) taking only a moderate amount of food and ale, and spend the rest of your money on cats.
Have your miners dig out a bedroom, a dining room, and an area for a few workshops, and then head for the river. Meanwhile, have your dwarfs build a bed, a chest, a cabinet, a throne, a table, and a whole bunch of doors. Oh, and at least 6 coffins. If your mason, carpenter and miners are skilled it will help things go more smoothly, and leave her with nice furniture. Keep the access to the river narrow enough that it can easily be blocked with doors, and then send everyone but the cat lady over to the river, and lock the doors behind them. Your miners can continue to dig out along the river bank, creating space for herbs to grow and perhaps a little nile farming, but keep the space long and narrow along the bank, so that everyone gets washed into the river during the summer flood.
Your cat lady will need to have all the skills (or at least the jobs) necessary to survive on her own. Having Herbalism, Cooking, and Brewing at high skill levels will make it easier to keep her fed and happy. You could also give her some optional skills like Fishing, weaving, cloth working, and other skills you think may be useful in the long run, but be prepared to turn the jobs on and off manually, so she doesn't spend all her time catching fish and then gets mad because there is no ale. Some skill in masonry would probably help too, since she'll need to build more coffins if the cats start to die off. Arranging to keep an axe and a pick with her may be helpful in the long run. Obviously the cat lady doesn't actually need to be female, but he or she should like cats. You want the cat lady to be safe, happy and self-sufficient, so that the cats will be happy.
Failure to build a trade depot should keep any caravans sitting on the west edge of the map, out of the way. Or you can trade with them, or even build traps to destroy them, it doesn't really matter. Immigrants can be a bigger problem, you don't want a bunch of smelly dwarfs cluttering up the cat fortress! You can either try to keep them out with locked-but-pet-accessible doors, or lock them next to the river to get swept away by flooding, or even build a drowning room for them. Whatever. If sieges get to be a problem, just move the cat lady across the river, and then retract or destroy the bridge.
Your feline population should grow at a good rate, until you have hundreds of cats and a lone dwarf living happily in their oft miasma'd splendor.