Well yeah it’s possible to use all the content from different templates/projects in a project. Everything from the content browser can be migrated to the project you choose. And so that’s the option you want to look for; right click in the asset you want to “export” to your own project and look for “Migrate”. It’ll automatically search for any asset connected with the one selected (e.g. you want to migrate a material and this will find any texture used in it, etc) then just click ok and it will show you a select folder window where you have to select the “Content” folder inside your project (this is the folder where everything will be migrated, following the same folder hierarchy you have in the actual template).
Sound rather simple but be cautious when migrating too much assets because sometime you can run in the “found asset with the same name” problem for assets that are different but share the same name. You can easilly end up with so much assets messed up and not working as it should. A tip would be to rename everything you migrate from one template before trying to migrate from any other.
About your other question; well first you’ll need the indie license from daz if you plan to use those models commercially.
Then you’ll probably want to decimate those models (inside daz there’s a tool to decimate meshes, you can get a decent result with it but is probably better to just retopologize it in an external app).
After that all you want to do is to go to file/export and select .FBX, then select a name for it and in the FBX options window you can select what you want to export (figures, objects, cameras, lights, etc).
And also you can select to only export visible objects (this way you can hide whatever part of the body of your mesh is hidden with clothing).
You can also select if you want to recollect all of your textures inside a folder in the same place where you export your FBX.
Finally you can also select if you want to export the morphs (but get ready for long LONG times importing your FBX inside UE4 if you decide to turn this option ON)
And i think that’s the important part in daz. The rest of the process is pretty straight forward as all you have to do is the same you would do with any FBX you want to import inside UE4.
Hope this helps.