I bought this rhododendron at Walmart the other day and want to train it as my first Bonsai specimen, but first want to thicken its trunk before putting it in a training pot with real Bonsai soil.

I know that azaleas require specific fertilizers and soil, and i was thinking of putting it either in the ground near my house or in a large pot I have to let it grow out with the soil and fertilizer shown in the attachments. It's currently sitting on a stool in a semi-shady semi-sunny spot.

If you have any tips and/or thoughts, please share them. Thanks!

In that pot it will most likely drown, as it is way too big. So you have to be very carefull watering. Better to take a pot noe or two sizes up and once it has filled that with roots, take one size up again.
Best would be full ground, semi-shade.

I see. I didn't even think of that. I will probably just grow it in the ground, then, if it's the absolute best option. Would I still need azalea soil to surround where I plant it?

The ground is best for thickening the trunk. Azalea grow best in acid soil. I would mix acid soil with some of the soil in your garden. It's not necessary that there is written "Azalea" on the package. Peat moss is acid.