If you have a single product to pass then you can use the extension in
Launch but if you have multiple products then the option is not there.
You can use custom code in that case. You can get a brief idea from here
1.Yes it is possible2.Yes it is possible and after from this You can use
Full processing Data Sources to upload offline data into Analytics.3.For
offline:Once the Data Sources wizard complete ,it will provide a
template to download and accordingly you can upload data.4.Totally
depend on implementationRegards,Shamshul AzamAdobe Marketing Cloud Team