Hi and welcome!
Having a spaniel was on my bucket list (

) - I'm now 64, so decided last year, its now or never!
I read loads beforehand and the only thing that did concern me was the amount of exercise etc he'd need, but also learned (on this site) how important mental stimulation is. By the time last winter arrived, which here at least must have been the wettest most dog unfriendly on record

, Humphrey was around six months old and outdoor activities were very limited. Mental stimulation, just hiding things for instance, would tire him out quicker than a half hour run.
Maybe we're just lucky, but apart from the odd "zoomie" in the evenings, I can't say he's hyperactive, he gets one good long walk in the mornings for about an hour, a training class once a week and a communal dog walk once a week, inbetween those times he's in and out of the garden and we'll have a bit of play. Having had other dogs before, all lovely, I can honestly say this little cocker has stolen my heart, friendly, fun and desperate to please. Walking nicely on the lead isn't a strong point but can be managed with training and, for those who like them, an anti pull harness.
As for leaving them alone, they are dogs who like company, but there are people here who work and have managed to find a compromise - i.e. dog walkers, day care etc. I believe its the quality of your time they receive not always the quantity that counts. You'd probably need to ensure someone's around regularly for the first few weeks however, until he's housetrained etc.
You'll get loads of support on here and there's always an ear willing to listen! Keep us posted and look forward to seeing pictures if and when your cocker baby arrives!