Question on Ultra HD TV and Netflix

[Ericandblueboy]

So I'm thinking about buying a 4K TV.  I understand that I need to upgrade my Netflix plan and get a Ultra HD streamer, such as Chromecast Ultra.  If I only have 1 4K TV, and the rest are just normal HD TVs with regular Chromecast, can I stream HD to my HDTVs and Ultra HD to the 4K TV?

[Keithstg]

Yes

[Ericandblueboy]

So I went to Best Buy to get a 4K TV.

Me:  I like to see 65" 4K TVs under $1,000

Saleslady (4 feet tall woman):  We don't have any

Me:  Your website shows 4

SL: Oh, let me check our website (she finds 4, Samsung, LG, Vizio, Hisense)

Me:  I'd like to see the Samsung and LG

SL:  They're not on display

Me:  So I'm supposed to buy a TV sight unseen?

SL:  You can look at similar models

Me:  So are all these displays showing 4K content?

SL:  Yes, the manufacturers wants to show 4K content

Me:  But there's no 4K content on cable, so I'd like to see how these TVs look when they upconvert HD programming 

SL:  We only have 2 TVs that are showing regular content and they're in the Magnolia room (where they sell really expensive TVs, we go look at one and its price is $3,600)

Me:  How do the speakers compare between the Samsung and LG

SL:  They're all terrible

Me:  Ok, I'll take the Samsung

SL:  Do you need a service plan

Me:  No

SL:  If the TV breaks down, with the service plan, Best Buy would come to your home and fix it, otherwise you'll have to deal with Samsung

Me:  That's alright

SL:  You need 4k HDMI cables

Me:  Why can't I use my existing HDMI cables

SL:  They would work but the quality would suck

Me:  Show me your 4k HDMI cables (the cheapest one turns out to be $30).

Me:  I'll pass on the 4k cables

SL:  Most people get a new receiver with their new TV, would you like a new receiver?

Me:  Um....no.

This maybe just my bad luck with one salesperson at Best Buy, but I suspect they're mostly clueless.