Hi Pete and a welcome to you and Poppy. Spaniels are a breed to themselves. Busy, full of love, keen as mustard and so much fun. When we got our first working girl at 10 months old, we also were uninitiated into their world. We wanted her to work in the field with us and trained her ourselves, by gleaning information from everyone and from all sources. We are a great fan of country shows, amazing how much help you can get from them. Gun dog training is a good way go go. It will get you the basics and control. You can also do the exercises in the home. Keep the training to short periods, they get overtired and lose concentration. Do not get cross or shouty, they are sensitive dogs.
We lost our Gemma in July, but next week Miss Molly will join the family at 10weeks old. Its over 30years since we went to puppyhood, so you are not alone in this new lifestyle.
I have to admit now we're a couple of months into ownership I'm not seeing "over tired" unless I'm not recognising it. Poppy has energy for days and weeks. I have heard that they become what you train them to be. The gun dog trainer told me to reel in the running and ball chasing over open ground as basically I'm training her to be an ultra-marathon runner and I would need to try to keep up! Also, as she gets greater confidence, she would be more likely to bolt and go missing, so I stick to hunt simulation in undergrowth, keeping her close by with whistle control. The gun dog trainer hates retractable leads and told me to bin mine, but I have found it useful when going to my son's football matches and when near roads, I'm hoping that in time Poppy and I will develop the type of connection that can replace the lead entirely, we're getting there I can see she watches me intently and my body language and where I'm looking and follows hand signals quite well but for now it lets her run close by and "quarter" and gives me the control failsafe. Now at 7 months she is really bulking up and being quite short haired with minimal feathering I can see she's all muscle, she's becoming quite a "unit".