here's some basic info about royal caribbean's suite perks:
http://www.royalcaribbean.com/contentWithHero.do?pagename=enhanced_program_for_suite_guests
no separate deck, but the suites are higher up. i think the junior suites may be on multiple decks, but those do not get concierge/true suite privileges; true suites are on the top decks.
there is a concierge lounge. the lounge on liberty is fairly similar to the one on the disney dream (but without the cartoons playing!
). they have snacks and a pre-dinner happy hour.
private sun deck depends on the class of ship. i think there is one on liberty, but i can't remember exactly where it is - i think it's one deck up from the pool, not right next to the pool. again, not that different from dream, though you don't access the sundeck from the lounge. don't hold me to this, though - i know for sure that oasis and quantum class have suite decks, but can't remember 100% about liberty.
something to keep in mind is that there is only one concierge on liberty and he's only in the lounge certain hours (though it's a good chunk of the day). i felt we got more personalized service on the dream because of this. however, our royal concierges have always been great, and have done everything we needed; it's just not always as convenient to get in touch (they give you their phone number, but i hate to call and bug them).
also, there will sometimes be extra, non-advertised perks. you'll get treats in your room like cheese plates and pastry plates a couple of times. sometimes there are suites-only activities, like on allure we got to do a sailaway from the helipad in front (normally closed to guests on that class of ship), and on anthem we got to do a suites-only ride on the north star. i can't remember if we got anything like that on liberty.
as for your other questions:
the solarium at the front of the ship is adults-only. it's a nice area - a pool and a couple of hot tubs, and lots of chairs, including big comfy chairs and loveseats, and i think even a couple of bench-type swings. most of it is open to the air. again, fairly similar to the dream adult area, though i think liberty's pool is bigger, and has some barstool-like seats in the water so you can sit. liberty was just given a major refurb a month or two ago and i was on it a couple years ago, so i don't know if anything has changed due to the refurb.
i haven't been to the spa. i don't think there's a rainforest room, but i think you can get day- or week-passes to the sauna/shower areas. not 100% sure. sorry.
as for charges, unlike disney, royal charges for soda. you can get a soda package for about $7 or $8/day if you want soda, and it's good at any bar, the dining rooms, and the coke freestyle machines. royal also has a casino. other than that, the charges are the same as disney - spa, bingo, shore excursions, tastings/mixology classes (and liberty also has a cupcake decorating class for a fee), alcohol (though there are drink packages), specialty restaurants (very good, but keep in mind they do allow kids in, unlike disney), fresh o.j. in the morning, specialty coffee drinks like starbucks-ish coffees similar to the cove cafe drinks, onboard souvenir and jewelry shops, etc. on one of our liberty cruises i had a bill of $5.
there is an automatic gratuity/service charge like disney does, and about the same price - i think it's $13/night per person for non-suites, and $15/night for suites - and you can choose to prepay it at home before you go or pay it onboard. overall, other than the soda, i don't find the charges any different than what's on disney.
i hope that helps!
