From a science-based approach, here are three sources from Dr Linda Chalker-Scott from Washington State University Extension that will give you more information. Note that she's approaching these topics from an urban gardening (in the ground, not in pots) perspective.
- On Phosphorus in the soil
- On organic material to soil ratios
- On foliar kelp extracts. Note that she does not address in-soil kelp, which is just another type of (often expensive) organic matter.
Now for some anecdotal information... Personally, I grow my seedlings in a commercial (i.e. used by the nursery trade) soilless potting mix that contains at least 50% composted material and bark. For plants that will be in pots over the growing season, I'm cheap, so I've begun using my own topsoil (which happens to be extremely well-draining, with excellent soil structure). I mix it (while lightly damp) with perlite in approximately a 7:1 soil to perlite ratio. I mix in the perlite to improve drainage even further. I then mix the resulting topsoil-perlite mixture with the soilless potting mix in a 1:1 ratio.
I only recommend using topsoil in your mix if it is excellent soil to begin with. No clay! You could get by with a sandier soil, in which case don't use much or any perlite.
So, to answer your question in bullet points:
- I think your two-part mix is okay, but I strongly recommend that you incorporate some material like perlite to help with drainage if you use topsoil (see next bullet)
- Only use excellent topsoil. If this is not available, then use a good commercial (if you can get it) soilless mix. By "commercial". I mean the one a local plant-producing nursery uses, not a bag branded by Miracle Grow or any other mixes avaliable at box stores.
- Only use well-rotted composted organic matter
- Be prepared to redo your pots every growing season
- Skip the bone meal (you should get enough phosphorus from the soil/compost)
- Skip the blood meal (you should get enough nitrogen from the soil/compost)
- All containers MUST contain drainage holes. To keep the soil from coming out of the hole(s), cover the hole(s) with a piece of paper towel when you put the mix in. This will quickly rot, but by that time the soil in the pot will have become firm enough where it will not come through the holes. Under no circumstances should you put gravel or any other material in the bottom of the container before you add your soil mix.
One last thought - you may want to consider submitting your final soil mix to a local lab for a soil analysis. This will tell you the percentages of major nutrients in your mix and will show any difficiencies. Depending on the lab, the test may also give you strategies to mitigate the difficiencies. This will allow you to fine-tune your mix for next year. In the US, I think all states run Extension programs that allow residents to submit soil samples for testing.