Hi Kim, welcome to
RP.
For a quick way to soften the edges of your cutouts, try the following.
Ctrl+click on the cut out layer to select it.
Now Select/Modify/Border and set radius to about 2-3 pixels.
Blur using Gaussian Blur (adjust radius for effect).
This should help your cutouts sit better into your image.
Halos can sometimes be removed by creating a layer above your cutout layer, set to colour blend, then sampling colour from the background, paint along the halo helping it to blend in. Not recommended for complex backgrounds where frequency of colour sampling would be too time consuming.
Hope this helps.