Reddit mentions of Maestro Acc-SAT-TO2 Sat Radio and GPS Antenna adaptors for TO2 Vehicles

• Maestro RR that handles communicating with steering wheel controls and CAN bus (https://www.amazon.com/gp/product/B00E4W1644/ref=ppx_yo_dt_b_asin_title_o04__o00_s01?ie=UTF8&psc=1)
  
• TO2 harness to tie the Maestro RR into existing wire harnesses (https://www.amazon.com/gp/product/B01K02TMKQ/ref=ppx_od_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)
  
• sTO2 to retain factory GPS and Siruis XM antennas (https://www.amazon.com/gp/product/B01K03PORU/ref=ppx_yo_dt_b_asin_title_o04__o00_s00?ie=UTF8&psc=1)
  
• PAC USB-TY1 to retain factory USB (https://www.amazon.com/gp/product/B00F0YJ49O/ref=ppx_yo_dt_b_asin_title_o04__o00_s00?ie=UTF8&psc=1)
  
• Metra 40-LX11 antenna adapter (https://www.amazon.com/gp/product/B003VYWSES/ref=ppx_od_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)
  
• Sirius XM tuner is OPTIONAL! You don't need this if you don't subscribe. (https://www.amazon.com/gp/product/B00NJTO4CY/ref=ppx_yo_dt_b_asin_title_o03__o00_s00?ie=UTF8&psc=1)
  
• Metra 99-8251B dash kit (https://www.amazon.com/gp/product/B01BTSW5YA/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1)
  
  And then obviously pick a head unit. We've had good luck with the Kenwood DNX695S, which has navigation, wired android auto, apple car play, and plays DVDs. It looks like a lot of parts but the only wire connecting you'll need to do is with the various harnesses listed above, and there's good documentation on what goes where. Once you get your harness all connected up, everything just plugs right into your existing Toyota harnesses.

If you want it to be easy as possible, you can use one of these (and you'll need to pick up a maestro sw or rr):

https://www.amazon.com/AutoHarnessHouse-Aftermarket-Installation-compatible-2016-2019/dp/B07GD8627K/ref=sr_1_1?keywords=autoharnesshouse+brz&qid=1573219865&sr=8-1

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That covers the steering wheel controls and camera, antenna amp, and factory amp. You'll need to add a pin and wire on the harness (it's included) to power up the factory amp and door speakers. Also, ignore the instructions included on the two 5-pin connectors - just connect the two on the harness together if it's not shipped as such. If you want to try to keep costs down and make your own, you'll need to wire in a voltage converter for the camera power feed.

You'll also need the standard Toyota harness for the rest of the speakers. You can use one of AutoHarnessHouse direct connect Pioneer ones, or just make your own a little cheaper. I believe this is the part, but please double check - I don't have the part number handy right now (You can actually get these at Best Buy, it's in their computer system):
https://www.amazon.com/Metra-70-1761-Wiring-Harness-Speaker/dp/B0002BEQJ8/ref=sr_1_1?crid=344R0OVLJ7ACT&keywords=metra+toyota+harness&qid=1573220037&sprefix=metra+toyo%2Caps%2C155&sr=8-1

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For the 4500, I also recommend either wiring up their GPS antenna, or just using an adapter for the OEM one (I went this route just to keep things clean). This pack contains the correct adapter (it's the one with the bright green end, maybe you can find it standalone cheaper):

https://www.amazon.com/gp/product/B01K03PORU/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

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If you don't hook up the GPS antenna, the head unit will throw up an error message every time you start up a navigation app in AndroidAuto (it'll still work, it's just annoying).

Lastly, don't forget an antenna adapter and (optionally the OEM USB port adapter cable). I opted not to use the USB port since I have a high speed charger that uses a 12v socket. Same as above, please double check this to make sure it is the right one, but here's what the antenna adapter looks like:

https://www.amazon.com/Metra-40-LX11-Antenna-Adaptor-Select/dp/B00JYHSDKO/ref=sxbs_sxwds-stvp?keywords=toyota+antenna+adapter&pd_rd_i=B00JYHSDKO&pd_rd_r=aae8b955-0220-497c-bcd6-480183748bd8&pd_rd_w=bmQ4P&pd_rd_wg=7ZU9O&pf_rd_p=a6d018ad-f20b-46c9-8920-433972c7d9b7&pf_rd_r=F20PSH58JCQN60PP1T5G&qid=1573220626

You'll need to wire in the blue wire to power the antenna amp. Don't hook it up to a constant 12v feed (yello), either use a switched feed, or wire it to the matching blue feed on the back of the harness (it's the one that feeds out of the two pins jumped together by a blue wire).

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Sorry I can't be 100% on the last couple of adapters - if you have trouble confirming feel free to DM me and I will be happy to check when I get home from work, I kept the packaging for later reference, and again, Best Buy does have these in their computer, so even if your local one doesn't carry them, they should at least be able to give you the part number.

This might be an elaborate way of answering your first question, but mostly I wanted to write out my experience of doing this exact thing. Also apparently I need to split this up into 2 replies.

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I have an AVH-W4400NEX and a 2012 Prius Plug-In. After buying all the stuff I needed...

• The head unit
  
• Maestro ADS-MRR
  
• Maestro HRN-RR-TO2 Plug and Play T-Harness for TO2 Toyota Vehicles (this will be different for other cars)
  
• Maestro Acc-SAT-TO2 Sat Radio and GPS Antenna adaptors for TO2 Vehicles (this will be different for other cars)
  
• Metra 40-LX11 Antenna Adaptor Cable - Select 2009-Up Lexus/Toyota (this will be different for other cars)
  
• AXXESS AX-TOYUSB - USB-Auxilliary Retention Harness - USB adaptor to retain the OE USB in select Toyota vehicles (this will be different for other cars)
  
• Metra 95-8226B Dash Kit for Toyota Prius 2010 Double DIN (though I actually went with the OEM Toyota one as it looked better, link here for reference)
  
• A nicer mic
  
• Audio tuner mic
  
• Some giant spudgers
  
• I'm sure I'm missing something else here, but eh.
  
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  I believe I set aside a Saturday afternoon to swap it out myself, and also install a dash cam with both front and rear cameras (the car already had backup camera built in). I ended up working on this through all of the weekend, and then did some more tweaks the following weekend.