no receiver - what sonos system should I buy?

Unfortunately, no Sonos component will work with the existing 5.1 speakers; a Connect Amp will be able to work with just the 2.1 part of these. If you want to continue to use them, you need to get a new receiver and a Sonos Connect to wire into it for a Sonos interface in both directions - to and from the interface to other Sonos speakers. The Connect is expensive compared to the price of a new receiver; many very good ones can be bought for less than the price of a Connect these days.

If you then add Sonos play units to the other rooms including the patio if it is well protected from the elements, or if you bring that speaker in when listening is done, you can hear music in more parts of your home, including the sound from the TV connected to the receiver. There will be some small sync delays, but it won't matter if the sound from the TV room does not leak across to the other places.

As a more permanent solution to the patio, you would have to install outdoor speakers there that are wire connected to a Connect Amp placed indoors, but near to the patio to minimise the cable run.

All of this needs the foundation of stable WiFi environment and a decent internet connection - the former is a must.

Well, yes, and no.

You say you want to continue to use your surround speakers, which can be done, but then you say you want to use your existing 5.1 speakers, which is problematic.

Sonos has one family of devices that can deal with a 5.1 signal, the PLAYBAR or PLAYBASE. None of their other devices currently have that ability. The PLAYBAR/PLAYBASE acts as a center, right and left speaker. But you could use that, along with a CONNECT:AMP to push your rear surround speakers. In fact, there's an FAQ around that: Setting up CONNECT:AMP as surround speakers

Sonos doesn't make an outdoor speaker per se. You could potentially use another CONNECT:AMP to power a set of outdoor speakers, there are many on these boards who have done so. If your patio is covered, Sonos does have the PLAY:1 and Sonos One speakers which are humidity resistant. I'd feel comfortable in putting them in a covered porch, but not outside in the rain.

As to your bedroom and kitchen, it's your choice. I have a pair of PLAY:1s in my kitchen, but lived comfortably for many years with a single PLAY:1 (and then a PLAY:5) there, before finally moving to wall mounts and the PLAY:1s for full stereo effect. In my bedroom, I happen to have a pair of PLAY:3s set up in stereo, but could easily have gone with a single PLAY:1, or a PLAY:5 too...it just depends on how much listening you do there.

The nice thing about the Sonos system is that you don't have to buy it all at one time, you can add to your system as the need arrives. And if you purchase from the right company (like Sonos themselves), you often can get a 90 day or longer return policy so that you can test out a device and see if it meets your needs.

The simple fact at the end of the day is that which speaker is right for you depends on a number of personal things, varying from what kind of music you listen to, what volume you use, and how your own ears and mind hears things. There's no "right" answer than anyone else can give you, it is your needs that are essential.

Best of luck!

Edit: Kumar beat me to it 🙂

Never mind Bruce, the two posts together make a more complete answer!

thanks folks. I think I understand. Just to clarify, if I purchase (call this Plan A) the 5.1 PLAYBAR/PLAYBASE package, I could avoid purchasing a receiver as long as I connect the PLAYBASE/BAR to my HDTV with an optical chord. The 2 PLAY:1s or Ones in the package, would also each need an electrical outet(s) if I decided to swap out my existing wired rear speakers. With Plan A, I could also reuse my rears in a separate room (and/or fronts or mid channels) if I also purchase CONNECT or CONNECT AMP (not sure I understand the difference), however does the CONNECT/ CONNECT/AMP require a receiver?

Plan B, for my HDTV room, to get 5.1 with my existing rears, I would purchase a new receiver, CONNECT or CONNECT/AMP, and PLAYBASE/BAR?

Separately, what does the SUB physically need to connect to?

Plan A sounds mostly right. The Connect:Amp is basically a Connect plus an amp. Therefore the Connect:Amp needs only a pair of passive speakers, the Connect also needs an amp.

Plan B doesn't fully make sense. If you purchase a Playbar/base and a Connect:Amp you don't need a receiver.

By SUB do you mean the Sonos Sub? If so then this connects wirelessly. You cannot use any other sub in a Sonos 5.1 setup.

Further points in addition to my previous post:
1 You cannot use a Connect and receiver for rear surrounds.
2 There needs to be a wired network path between the Playbar/base and Connect:Amp. Personally I would say go with a pair of Play:1s