Savinelli 315 KS, Savinelli 316 KS, or.....

Ha, it's almost like you were calling me by name!
I have Savinelli 305's, 315KS's and 316KS's exclusively and also like 20-30 smokes, which is one of the reasons I gravitated toward these pipes.
The 316 is a tad on on the large size and you're going to get more than a 20 minute smoke from it.
The 305 is smaller and has a conical chamber, will work for what you want, but again, on the small side.
The 315KS is in the Goldilocks zone. It's the perfect size and shape as far as I'm concerned. I love my 315KS's and that would be my recommendation.
There's also the 313, which is really just a smaller 315, which is also a good choice, but like the 305 is a bit on the small side.
Also, just my opinion again but if you're going to get a new Savinelli, get one of the midrange to higher end models like the Monsieur, Fuoco, or Punto Oro, and stay away from the lower end lines like Roma and Oscar Tiger.
Not that there's anything wrong with them, all Savinelli's are good, but if you're getting a Savinelli, you might as well get a nicer one and spend $150-$200. And, I'm not really that big a fan of rustication. Get an actual sandblast if you want that look. My 315KS Monsieur sandblast is probably my favorite pipe.
The one issue you mention that you may have trouble with is clenching. I don't do it myself so it's not an issue for me but none of these are really clenchers, especially the 316. The 305 is probably the best option for clenching of the shapes mentioned so far.
If that's a huge issue for you, you probably should look at something like the 623 or 626, and maybe even the Savinelli petite or pocket models. Plenty of great pipes to choose from in those lines as well.

Not sub quality, probably not the grain they would want in an upper grade pipe. I think all mentioned clench beautifully, but my favorite design for effortless clenching is the 904, though the chamber may be a bit deeper than you like.

the stem part got loose after a while for some reason

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There are actually a few easy fixes for that.

Not really. A bowl coating is supposed to aid in breaking in a pipe, but is totally unnecessary.

I think Savinelli uses the bowl coating to hide flaws. Just my opinion of course, but I base that on the fact that all lower end models have the coating, some mid grade models, and no higher end models have the coating. I personally don't like it and don't think it helps and in fact may even taste a little odd.

also i noticed that some pipe's bowl have pure wood inside while others have a black coating, should that be a consideration when buying a pipe?
https://www.tobaccopipes.com/savinelli-roma-315-ks-black-stem-tobacco-pipe/

https://www.tobaccopipes.com/savinelli-fuoco-rustic-315-ks-tobacco-pipe/
this fuoco is actually at a decent price (pure wood bowl itnerior as opposed to the roma's coated)

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One thing to keep in mind is that tobaccopipes often uses "stock" photos and the pipe in the pic isn't necessarily the one you will get. And as I mentioned above, on the mid range lines, sometimes there's a bowl coating and sometimes not, so you're probably rolling the dice buying a Savinelli from them if the bowl coating issue is important to you.
I like buying from smokingpipes.com. They always show you the exact pipe you are getting.

I base that on the fact that all lower end models have the coating

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Most of the Marte line have no coating, and pricewise, I would consider them entry level.

I agree with everything seacapt said, with the exception of the lower level Sav lines.

I think it’s probably more useful to but the cheaper lines until you really narrow down the shape you want.

I personally prefer the 305, and an estate Roma 305 I got for 40 bucks from smoking pipes is my best smoker hands down.

You can’t go wrong with any of those models mentioned, and there certainly is something to be said about the quality and beauty of the mid level and higher Sav lines too!

The Marte line is one of my favorite looks... sharp!

Most of the Marte line have no coating, and pricewise, I would consider them entry level.

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Personally, I was calling the sub $100 lines as lower end, $100-$150 mid range and over $150 upper end. I don't think I've ever seen a Savinelli above $150 with a bowl coating or a sub $100 without one.
By that definition, the Marte would be mid level and hit and miss on the bowl coatings.

I don't think I've ever seen a Savinelli above $150 with a bowl coating

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Punto Oro

I figured you'd find one.
Still, it's pretty unmistakable that lower end pipes have it and upper end pipes tend not to.
If the bowl coating isn't to hide flaws, then what's it for? And if it's "good", then why isn't it used consistently across lines?

Not sure. I just posted a Punto Pro because both of mine had it as well. They may be catering to people who prefer them. I do like the burning briar taste of a virgin bowl, but have never been put off by a bowl coating. Some pipes just look "finished" with a black chamber.

And I regret finding that Marte. Might have to buy one.

Back to the OP's question, this 623 might fit all your criteria.

Great looking piece and good specs.
623

Not to be Mr. Contrarian but, I have a Savinelli Spring 678 that came without a bowl coating...Right at $100.00.
As well, I had a Trevi 606 that sold right at $80.00 or so without the coating.