Advice for a TV please

For me I have a Sony Bravia Android TV. It runs pretty much anything you can get off of the Playstore plus Aptoide.tv apps.
Kodi runs great as does the IPTV trials I tried. Sony may be out of your price range and that's cool. As for custom firmware or root I'm not sure. Sony keeps their source code locked up. There was no problem trying out an X900 for a week and returning it for the X930E I now have. There were some bugs that Sony did iron out after awhile in a firmware update. Best thing is to look at reviews really. Some of the cons people list may be valid, or they may be expecting just a little too much.
Since your plasma is a bit dated I guess, the Android OS will be a nice experience. I weighed my decision between Samsung and Sony. Since they have been good for me over the years I chose Sony again. You may consider an extended warranty and definitely a very good surge protector in your budget.
One nice thing too is CEC which keeps you from hunting input sources. Pick up your Fire TV, Roku, or sat box remote (or Harmony, universal) and hit a button and sources switch right away. Since most every tv accepts that you're going to use a soundbar or audio system (they have crappy internal speakers)....put that into your budget too.

Edit:
Oh yeah. Grab a bluetooth keyboard and mouse too. Your remote will thank you!

I don't think you can really go wrong with any modern tv nowadays.

I always buy my TVs from richersounds. Get some great deals on there.

Tip: Join richersounds and become a VIP member. Get even better deals.

I normally go for lg but would consider anything within price range really.

I prefer a basic non smart tv but they are becoming scarce.

A good android box will take care of all the smart stuff, kodi, iptv etc.

A soundbar with most modern tv's is a must as the onboard amplifier / speakers are normally crappy.

Quote from snifferhann

Thanks for that guys. I did walk into Currys and liked the look of a Sony, the picture looked excellent, but thought I best check in case there was a certain brand that was open to manipulation. Will have a look what deals I can find around.

Good luck in your search and choice. Codar mentioned a non-Android (smart) TV. I didn't even know that 4K TV's not "smart" existed. But a search of Bestbuy over here showed them. At a price. 8K TV's are starting to populate the market. But with the limited 4K content out right now I'd certainly weigh heavily pondering one at this time (8K). I perform bench repairs so serviceability in the future is very important. Probably why one reason my choice was a name brand with good probability of future parts sourcing. I'm seeing many of the lesser brands using....'supermarket' parts. A screen from this guy, a main board from another, etc. Just had to add this.
Samsung is known to have excellent PC monitors and Sony engulfs the broadcast industry. LG makes good video products but they also make blenders and air conditioners. You get it.