Hi Squish, I am new too, and probably not very well-equipped to handle your questions, but I have been reading this forum a lot lately, and have been doing a fair amount of research, so here goes. Bear in mind, this is kind of like the blind leading the blind.
As Peter said, the seam is typical, and I thought I would find it bothersome, but I really don’t. If you think it’s going to give you a blister or callous, I think perhaps you are gripping the whistle too hard. It’s as light as a feather and you don’t need to grip it tightly. My first whistle (and ONLY whistle until yesterday when a package arrived from Jerry Freeman) is the Clarke Original, so I’m well acquainted with that seam and have been playing mine for weeks w/o any issue..
Getting a good tone is very much a function of practice. While it’s not quite as tricky as learning how to produce good tone on a flute, where embouchure plays a big role, I still think it’s an acquired skill. It seems like a lot of newcomers to this forum complain about either hitting the higher octave or the lowest notes. While it’s certainly possible you have a badly behaving whistle, I am guessing those higher notes will come in time. I think you can’t be afraid to attack them either, even if they are a bit scary sounding. They have to sound like rubbish before they have any chance of getting better.
That said, whistles are relatively cheap, and fun to collect. No reason to not pick up a couple others for comparison purposes. You may find another brand easier to play as a beginner and someday may come back to the Clarke and wonder what all the fuss was about. 
Having just received three new tweaked Generations, my initial impressions are that they require more air than the Clarke. I’m not sure if your background includes other woodwinds besides the recorder, but perhaps you are just blowing too hard. Maybe you are blowing harder than you need to for even for the 2nd octave and it’s making it sound especially shrill. Or maybe you aren’t really committing to hitting that higher octave because you are scared of the note that’s gonna come out.
I know that feeling too. My Clarke requires barely any air at all to play, especially in the lower register. That said, I do have issues going above the high G. It sounds horrid, but I know part of that is being new to it. One other big difference I notice with the tweaked Generations is that the two octaves play more evenly and are more similar in terms of breath requirement.
Based on your dislike of the seam and the difficulties with upper octave, you may find one of Jerry’s tweaked Generations (or any other non-seamed whistle) more to your liking. I was able to get into the higher octaves much easier on my new Generations than on the Clarke. I think being a newbie, it’s easier to just purchase a whistle from someone that can vouch that it will play true so you aren’t wasting your time beating yourself up on a whistle that may not be preforming at its best.
Regarding holding your fingers down, again, I think you just need to relax your playing style. Make sure you are using the pads of your fingers and not the tips. Some have recommended using lotion beforehand to help encourage a good seal. I am a woman with average sized hands and I’m not really finding it being hard covering the finger holes on the Clarke…the holes on that whistle are much smaller than some other whistles in fact!
I would practice just going up and down the scale really concentrating on getting good tone, and then jumping from octave to octave. Don’t expect to get all of the higher octave to sound sweet immediately, work your way into one higher note every couple days until you aren’t wincing when you play it.
Good luck!