No worries and so happy that your local nursery has suggested you simplify and use Osmocote as a fertilizer. The easy answer here is to use Osmocote Plus on all the plants you are growing and then after a year or so you can evaluate if your alkaline soil needs more help to release nutrients. The more important point you mention is that your soil does not have the best drainage so perhaps it is heavy in clay. If so, clay soil that drains slowly can cause poor root growth and rot during wet winters. The best fertilizer in the world will not correct this. You may want to consider improving your soil with organic matter such as compost, grass clippings and fallen leaves to improve the structure and drainage. A mulch on top of the soil will also to help cool the soil and seal in moisture. Try not to worry too much as you will keep learning more as your gardening journey continues. Losing a few plants as you learn is part of the journey. I suggest you take note of what grows well in your garden and then add similar plants. As your gardening skills improve you can become more adventurous in your plant choices. Keep us posted on what plants do well next year. Your landscape sounds like it will be lovely. Keep growing, Marianne Binetti