Driving home last night I realized I had some info that you guys may find helpful. I've haven't done Uniworld before but this is how it was on my 2 Viking River cruises.
Dress code: Very casual. I wear jeans/sweats during the day and for dinner business casual. I took 1 cocktail dress and it was more dressy than need be. They do have the captain's night and people dress a little nicer for that but no suit is required. Some people even worn jeans and tennis shoes to dinner (I don't, just personal preference - I'd rather wear dress pants and a sweater to dinner).
Liquor: They had a fully stacked bar on both ships. I'm not a big drinker and didn't order any mixed drinks but it seemed to be pretty extensive and reasonably priced. I recall (don't hold me to this) that a 1/2 carafe of the house wine ran about 5 euros.
We bought wine locally and brought it aboard almost everyday. The cruise line did not seem to have a problem with this and after the 2nd time we stopped "smuggling" it on board in the back pack. They do however have a $10 corkage fee they are "supposed" to charge for opening any bottles. The 1st cruise I was able to blink eyelashes at the bartender and wasn't charged. The 2nd cruise we took our own corkscrew and that was great. We would fill up before the talk in the lounge then refill on the way past our room going to the dining room. The plus of a small ship!
Luggage day of arrival: They let you store your luggage in the lounge until your cabin is available later in the day. They usually have a light lunch set out for a few hours, sandwiches and drinks, which is a nice perk. Same for last day - they will hold luggage for a few hours.
BTW, dress warmly. A lot of tours are outside walking and it's colder on the River than you would expect. I hope this helps some of you.