If you had to, you could use the black soap tip that might have come with your machine but there are many companies making those and the orifice sizes are not consistent.
It comes down to personal preference, I like to soap with the 1540 (threaded nozzles, no color plastic guide on these so they fit into the 2, 3 or 4 nozzle holders that the vendors sell so all your nozzles are together) and for up high, I like to use the 0050 with the 8gpm or 5.6gpm machine. I also have the 2540 nozzle on the 3-way holder but hardly ever use it, these 2 are what I use on just about all the house wash jobs I do and they work great. No sense in buying tons of nozzles if you don't need them or will not use them.
For rinsing I like to use the same nozzles for low pressure but great rinsing flow so you don't blow mulch out of the flowerbeds, don't knock hanging stuff down, etc.....I have to go back to the trailer and pull the soap hose out of the soap container to use the same nozzles but that is ok, that is how I like to rinse. I usually put the hose into a container of water to rinse out the injector so they last longer, usually get about a year out of the injectors this way.
My machines are only 3000psi, you can use the same nozzles if you want to. The smaller the orifice, the more of a "mist" you will have with the 00 nozzles, the larger the orifice, the tighter the pattern and less mist to a point, then the larger you go, the less pressure and less distance you get. I don't go lower than 30 or 40 orifice for pulling chemicals, smaller and it will not pull chemical, too big and there is hardly any pressure.
Most of the vendors out there sell the same nozzles and holders, pick a vendor you like, some have minimum purchases, many don't.
The first 2 numbers are the fan pattern and the last 2 numbers are the orifice size, you can look on the nozzle charts to see how they lower pressure, just always go by your gpm's and psi to see what orifice you need for your machine. Downstreaming is different, no real chart made for this, just experience and help from the guys on the forums will help you but this is enough info for you to get started. I would order some General Pump Hi Draw injectors (non-adjustable) as they will go out on you when you need them most and hard to find good injectors locally, especially without spending 3 to 5 times the price.
Good luck.