Yes you used "yalla" properly in every single one
and elhamdulilah is the spelling/pronunciation for the term in proper Arabic but in many dialects they shorten it to "elhamdela"
I would say Gulf accents are probably the "heaviest" of all accents.. extremely masculine sounding
Lebanese/Syrian - people from other countries like Palestine sometimes say that it sounds too "soft & feminine" lol but I think its a balance.. Probably the Egyptian dialect is the most "feminine" sounding since they drop alot of the heavier sounds like the "Q" and "J" becomes a "G"
Palestinian and Jordanian have similarities with the Leb and Syrian dialects but is a bit more masculine/heavy sounding to the ears.. I'd say that they're more nasally, but in the end I guess it's to each his own
Most people who are not from the Gulf area have difficulty understanding their accents and find it to be less enjoyable to listen to..
But each country has different accents within the country.. So in certain parts of Lebanon you may find someone saying the word "albi" (my heart) and in another part pronouncing it "galbi" its all based off location too, but for your book I'd take the majority/more commonly used term (in this case albi) so that it will be more widely understood