Hello Tfxx, and welcome to the forum.
Condolences on the loss of your dad, and good for you for taking responsibility for his remains.
Just to share a bit of my experience with houseplants. I've kept plants for over 30 years, and currently have quite a few. I've lost some and added some, there are only one or two that have survived that whole time. There are none that are in the same soil. They require re-potting every few years, with a complete change of soil.
So let me say this kindly but clearly: mixing Dad's ashes in with planting mix will not keep him and a healthy plant close to you for the long term.
I suggest getting started with a plant you can dedicate to his memory, but do something else with the ashes. Did he ever express any preference himself?
What are your growing conditions like? Cactus and succulents are actually somewhat difficult to grow indoors. Right now I'm leaning toward peace lily, they do great for me but some people to find them difficult.
Indoor gardening is a great hobby. Start slowly and find what works for you. This forum is a great place to come to for advice.
Best wishes to you, and welcome to our gardening community.
(PS My son recently vacationed in Perth, had a great time, he especially enjoyed the people of Western Australia, Rottnest Island, and the Quokkas.)
