There are lots of items you can add to Weight Gain Smoothie to increase nutrition and calorie count.
But to get you started, here are some guidelines:
Start with a simple, cheap kitchen blender. Most of us already have one of these in the kitchen. A basic blender will work with recipes that don't have a lot of solids that need to be blended.
Start simple using the following recipe and variations. (eliminate anything that doesn't agree with you):
Basic smoothie #1
First addition to Smoothie #1
Second addition to Smoothie #1 (to add some nutrition)
If you have a more powerful blender, consider adding some additional nutritional items. Start small and don't use all of these at the same time.
Keep experimenting until you build a list of ingredients and recipes that work for you!