You might consider asking this in the ENT and Uro rooms, respectively. I have no idea about uro-onc.
For Head and Neck, part of it will depend upon whether you're going to do your own microvascular or not. Most do. Some do not. If you don't, then you'll have a plastics guy laying free flaps for you, which really does improve your quality of life. You do the resection and the neck dissection, but you don't necessarily stick around for the free flap. That will cut your case in half. Plus, most of the difficult post-surgical care is flap-related.
That being said, free flaps are interesting, and most guys who go in to head and neck want to do free flaps. With residents, cases can run anywhere for 4-18 hours. In a private setting, I've seen resection, bilateral neck dissection, and free flap with micro and closure in 4-6 hours for moderately sized cancers. It can also be faster if you have a partner who does micro, and you have the financial ability to buddy up on cases.
You definitely spend time in clinic. How much is very, very practice dependent. Many Head/Neck guys outside of an academic setting get patients sent to them from other ENTs, so in many cases the cancer has already been diagnosed, and they're more or less ready to go to the OR. But, you'll still get internal referrals for "guy with big tonsil," with nothing done. Some guys follow their patients personally for five years to monitor for recurrence. A lot of them will have them follow up with a local ENT that's closer to the patient, if possible. Many of them (if not almost all anymore) have either residents or a PA because there's usually a lot of paperwork for social reasons, and those mid-levels can also screen a lot of low-risk problems with cancer patients.
A lot of Head and Neck cancer is primarily treated with chemotherapy and radiation - especially oropharyngeal, nasopharyngeal, and laryngeal cancers. Those all used to get surgery, but now most get chemorads. So in those cases you'll be treating a lot of recurrences, treatment failures, or patients with bad kidneys who can't do chemo. That being said, for some cancers surgery is still the primary treatment modality (oral cancers, salivary cancers, large skin cancers, sinonasal tumors excluding nasopharyngeal). Additionally, the patient demographic is shifting a bit. Everyone used to drink like a fish and smoke like a chimney. Those guys are still out there, but more and more you're seeing young (late40s-late50s) patients who never smoked or drank getting throat cancer (HPV). They tend to respond better to any treatment they get. which doesn't make much of a difference so far as the surgery is concerned, but boy are they easier to manage post-op. It's nice when they're healthy other than the cancer, rather than the horrible diabetic/vasculopath with four stents.
How many inpatients you have is also going to vary quite a bit. Most of the services I've been around with ONE micro-trained HN oncologist will have 5-10 patients on service at any point in time. Most are post-op, some are admits for other reasons. If you're at an academic setting, that number might be much higher.
I think your questions are hard to answer because these things can vary considerably depending upon how one runs one's practice (partners or not, private or academic or employed by a hospital, microvascular or not, are you also doing thyroid cancer, or do you let the general ENTs do that?).
I will say that it is hard (but not impossible) to be a private practice head and neck oncologist. The cases just don't reimburse well when you consider how much time they take in the OR and how much recovery time they take in the hospital. I do a lot of head and neck cancer, but I frequently send patients downtown not because I couldn't do the case, but because I'd be pulling my hair out and losing money if I did them.
As you said, first decide if you like the kind of surgery they're doing or not. I'd be really surprised if many people can compare these head-to-head. I don't know anyone personally who has enough experience in both to do so without a lot of guessing. If you like the D&B more than the throat, then go uro.