You just described my standard garden method. :-) I doubt that you would have an issue with moving things around except possibly the tulips.

Those gaps of missing mortar between bricks on the bottom course are known as weep-holes. They're there primarily to let any moisture out that accumulates between the back of the brick and the moisture barrier. Depending upon how/when your house was built, the ledge that the brick sits on might only be an inch or so lower than the main slab where walls and flooring reside. So even covering just the bottom portion of the holes is a bad idea since it can enable water to backup to the base plate. Amount of roof overhang, 1 story vs 2 story, and other factors affect how much water will penetrate and drain behind brick veneer... but it is a surprising amount. We learned about their importance when the builder's subcontractor inadvertently left them off our first house. A 2-story with no roof overhang made mess of our first floor carpets the first few heavy rains until the problem was identified and a mason chiseled out the weep-holes. Roselee's experience with termites entering these is very common and something a good inspector will warn about. Ours recommends keeping any soil or mulch at least an inch below the bottom row of bricks. We've had to regrade the uphill side of our house to accomplish this and get some slope away from the slab.

You'll need to remove the mulch in order to direct sow seeds (annual or perennial) or the mulch will prevent germination or growth and you'll need to keep the mulch off until stuff is big enough. I had to do this last year...such a pain and things were looking patchy for a while. You can also sow one type of seed in an area so you'll know what they are but keep in mind rain will wash things to other places and then transplant elsewhere...which is pretty easy to do and the little plants bounce back really quick. I would not mix annuals and perennials just because perennials are really slow to grow and really won't look like much for year 1. Annuals grow like crazy and you can sow them in a tray (even now) and transplant out in a few weeks so you don't have to remove the mulch and they will get big by late june and flower for the rest of the summer. I like salvia victoria blue, cosmos, alyssum, california poppies, and bachelor buttons. Post a pic when you can, would love to see the result.

One of the primary attributes of raised bed gardening is the ability to size the bed so that the plants can be easily reached and attended to without walking on the soil or actually invading the bed :-) Any time you do that, even with stepping stones or pavers delineating a path, you are compressing the soil and damaging its structure. In short, it is counterproductive to construct a raised bed so large that this would be necessary.