Lovely pup and sharp image
You can never have enough lens. Saying that , depends what you want to shoot. A 250 will be more than enough for general stuff but if you're into wildlife (small bird, mammals etc) then a 250 will seem inadequate. If not, then a 250 is fine for general shooting and bigger subjects. You can pick up used Sigma Contemporary or Tamron (150-600) for around £500-£600, both decent glass.
I used to carry a 150-600 Sigma (sport version) and whilst great for reach, it was impossible to hand hold due to the weight. Next to useless unless on a tripod or mono. Great lens though. Downsized to a 300 prime + 1.4 TC and I'm back to wanting more. Saving hard for the 500 prime and that will be the end of it.