Hi Roger,
Here's another page that might be of use for planning what birds are likely in Rio Negro province:
https://ebird.org/barchart?byr=1900&eyr=2019&bmo=1&emo=12&r=AR-R
It's for the whole province, and you obviously won't see birds in the wrong habitat, but it's a good way to see what to maybe expect on a higher level.
As far as field guides go, you have the only one. There is no other field guide for Argentina, unfortunately. To supplement, the Ridgely guide "Birds of South America: Passerines", and the Princeton guide "Birds of South America: Non-Passerines: Rheas to Woodpeckers" are the two best quality additions if desired, but carrying three books is obviously bulky and the second two cover a huge number of species that are not found in Argentina as well.
I don't know Horacio personally (Buenos Dias Birding) but he seems to have a good reputation from what I hear. Costanera Sur is plenty safe. As many parts of the world I wouldn't show your camera and binoculars around town but once you're in the reserve it's totally safe. Taxis to get to and from the reserve are safe, easy, and reliable, and operate with an electronic meter. I go frequently and have never seen or heard of any incident of any kind. Heading out of town to the Ceibas area will net you a ton of species and having a local guide does help out there - there are mazes of dirt roads and while the whole area is birdy, a guide will really increase the number of harder/special birds seen. I've birded out there a good bit but have also spent a fair amount of time wandering around exploring and still don't know where the stakeouts or best areas are for many of the harder species.
In Iguazu a local guide will certainly help you see more if you're not familiar with Neotropical rainforest birds and birding. If you wanted to bird for yourself, taking advantage of the "second day at half price" entrance to the National Park and hiking the "Macuco" trail is a nice birding site, with or without a guide for that matter. I don't know many of the guides in the area but Guy Cox (Toucan Birding) is a Brit expat and local expert who guides. The folks from Karadya Lodge also guide and have a good reputation. I'm sure there are more, of course, and just because I don't know of them doesn't mean they might not also be good!
Any other questions feel free to ask, happy to help.
Josh