As for the B737, it's most likely the PMDG NGX (which I don' have, but it sounds it is one of the best addons ever) or the iFly 737 (which I do have - it's a nice plane, but not as detailed as the NGX; however, you'll get a lot more versions for the same money).
As someone else said, there's only one Embraer 145 out there, and that's the Feelthere one.
For scenery, you can't really go wrong with FTX Global for now. If you're looking for airport sceneries, you need to be more specific about the area where you want to fly - there's simply too many airports available to say which ones are the best.
Other planes I can really recommend are the Realair Lancair Legacy, the A2A C172 and J3 Cub as well as the Aerosoft Airbus X Extended and the Majestic Dash 8 - all are excellent aircraft that look great and simulate at least SOP (applies especially for the Airbus, the others can simulate more I think, haven't tried that yet) very nicely.
As for the AI traffic, I'd ask you to search the forums a bit (or read through the threads linked below) - there are too many options, which all have their pros and cons, and it's been discussed too often. In short, my advice would be:
1.) Try World of AI and Military AI Works, both are freeware and were actually created for FS9, but they do work in FSX, and you can safe space on your drive by using only packages for the area(s) you fly in. Be aware that using FS9 traffic files will lose you all FSX native AI traffic, though, so if you want to keep ship traffic (and possible other AI traffic you'll need a tool such as AI Flight Plan Converter to convert those files to FSX format)
2.) Try Flight1 Ultimate Traffic 2, they got a 30-day-money-back policy for downloads, so you can try it with no loss.
3.) If you don't like either of the above options, you still have MyTraffic Professional (there are other versions, but IMHO Professional is by far the best) or Traffic 360 as well as the option to create your own traffic.
For further details, refer to the following threads(cross-referencing in those thread is possible):
I'd also recommend to buy REX Plus Overdrive to replace the default sky and airport textures.
That being said, welcome to Avsim! This is a great and helpful community, don't hesitate to ask if you need assistance, you'll always find someone who can help here. Enjoy your new hobby (and the forums, of course).