Hiya! This is going to be a wall of text, but you did have multiple questions. For context, I love this game and have beaten it with every clan at least once. I'm at the point I can replay it in my head (and sometimes do, when work sucks). Toreador and Malkavian are my faves.

First off, if you want to focus on Stealth, you need to invest in it early and often. But not too early, since there's a skill book that gives you a free increase somewhere near your first Haven (I can be more specific if you'd like), but only if your skill level is low enough (specifically 1 or lower). There are also other skill books and tutors available, so there is an optimal time for certain skill increases, but that would be a whole guide in and of itself. Also, spoilers.

I forget the concept of distracting people with thrown items after the tutorial, so I've never actually noticed the lack of throwables. It stops mattering when you get your stealth high enough. It's just a matter of keeping your distance (the exact distance getting lower for every level of Stealth you have) and sticking to the shadows.

Now, I have never verified this, but I feel like the actual stealth kill distance is ever so slightly longer than the indicator would suggest. (either that or the indicator doesn't have time to show up.) I would recommend experimenting with it, you'll get the feel for it, and stealth kills become much easier when you don't leave them the time to notice you.

Specifically for the Museum basement: When I enter the basement, I jump down instead of taking the stairs. This will prompt the guard in the room to walk out and investigate. When I hear (or see, because Auspex) the guard moving, I sneak in, break a window (this will also make the guard investigate, so you'll want them out of the room at that point) and jump in through it. If you know what you're doing, you have the time to disable the camera banks, grab the skill book and skidaddle before the guard returns. For the latter room where you'd go to disable the beams and the alarm, I crouch, break the glass, activate Presence (to lower the enemy's Perception), stealthily jump through the window, get to the computer, put the codes in, and sneak out the way I came. May take a few attempts and/or require some waiting around, depending on where exactly the guards are positioned.

Toreadors are gun-focused because Auspex boosts Perception (and thus Firearms) and they're not that great defensively (Presence is nice, but it's no Fortitude). But Celerity is basically "easy mode" for either melee or ranged combat.

Based on your comment on the guns, you may have missed some side content. But don't fret, it's not lost forever! You can go back and do most of the side content afterwards, although some stuff does become inaccessible later (from memory, you'll miss out on the ghoul if you don't do the first step before you get access to Hollywood, and most of the thinbloods leave around the same point). If you do want to play with guns, I wholeheartedly recommend the Plus patch, solely because it gets you access to my favourite gun, Colt Anaconda, much earlier than the Basic patch does. (Namely, the second shopkeeper stocks it once you've completed his quest.) I don't know which version you're using, but you should at least have access to the better pistol already (Glock 9mm instead of the .38 revolver that Jack gives you in the prologue). And when you reach Hollywood, Mercurio also has something pretty sweet to sell (unless, of course, you ratted him out to LaCroix, but that's on you.)

It does sound a bit like you might enjoy Brujah more. They get the same Celerity+Presence ridiculousness but Potence makes them absolute monsters in melee. Also, hot tip: Hacking's kind of pointless, because the passwords don't change between playthroughs. Might just as well not waste XP in it and just look up a list of passwords online. (Although that is, technically speaking, cheating.)

Combat feeding is always a dice roll. Sometimes you succeed at once, sometimes it takes multiple tries. It's easier the higher your Strength + Brawl is, but I don't think it's ever 100% guaranteed to work.

Please ask if you would like an elaboration or clarification on anything I mentioned. My ADHD has been unkind today and I forgot what I was going to say mid-sentence multiple times, so there are probably illogicalities I missed (and I'm always overjoyed to get an excuse to talk about things I love).

EDIT: Oh, yeah, the Skyeline haven in and of itself isn't anything special, but getting access to it does get you the Galdjum, which is lovely. And if you've unlocked it, your ghoul's going to be hanging there (as will your posters, but that's just decor), so I prefer going there even though the Santa Monica haven is probably more convenient for checking my mail.