The post spikes were not available when I did my elevated line and the concrete blocks with the cross slot in the top for holding a 4x4 post were just showing up, but were too expensive for me.
For mine, I already had several trapezoidal wall caps (1.5 to 2 inch thick concrete slab about 8 to 10-in. on a side) and a few 18-in by 18-in concrete patio blocks, so I started with them and bought a few more of each to complete my design. I drilled one 3/4-inch hole in the middle of the small blocks and two holes in the larger patio blocks (about 2 inches in from opposite corners).
I then placed them out in the shape I wanted for my line in an alternating pattern. The small blocks on the center line and the large blocks with the holes at right angles to each side of the center line. This gave me a triangular pattern of holes. The large block holes were about 22 inches apart and the distance to the single block varied at either 3-ft or 5-ft, depending on whether it was on a straight section or in the curves of the two loop-backs on each end of the line.
The image below is what I drew to figure out the layout. You can see how the small and large blocks were placed. The small numbers are the "mile posts" (not really scale miles... not even 1/10 miles, just "markers") and the larger underlined numbers are the height of the posts that I determined by using a home-made laser level line and a yardstick. (I printed the drawing, then went outside in the evening with my home-made laser level and all by myself aimed the level where I though I ought'a, went to the location, hunted for the laser beam, went back to move the laser, went back and checked again with the yardstick, oh what tedium... I eventually wrote down the number and then did it again for the next location. A rotating laser would have been LOTS easier, but I found an even better way to determine the lengths of the uprights during construction... I cut what I thought was the shortest post to length, attached the stringer that was to go to the next post, held it out with a level on it and measured to the ground at the end of it. I did not need to do all the pre-measuring. (Note also, I left out blocks 3 and 38 in the actual build as that section became just a 6-ft straight section in the reverse curve exit from the loop-backs.)
Anyway, the triangular shape of the structure gives SOME stability that just a post standing on the ground would give, but not nearly as much as a post sunk INTO the ground.
Oh, I should explain the holes in the concrete blocks. I drilled a 1/2-inch hole in the end of each post (axially) about 4 to 6 inches deep and then pushed the head of a 12-inch long "Landscape nail/spike" into the hole with a big glob of epoxy to hold it in. This spike acted as a "drift pin" in the hole in the concrete blocks and kept it from sliding off the block (and helped anchor the block on the ground).
This hole was also a part of a FAILED grander scheme to allow small adjustments to the height of the structure. I drilled another 1/2-inch hole in the other end of the post, again axially in the center of the post, about 6 to 8-inches deep. Into this hole I put a 3/8-inch "T-Nut". This is a device that has a threaded hole in a flange such that it can be pounded into the hole in the post and secured with a couple of small screws through the flange such to allow a bolt to be screwed into the post. Then if the post is spun on its axis (and the bolt held still) the bolt will be pushed in or out of the hole. I used a carriage bolt, attached to the bottom of a board using a metal light-switch cover... the square part of the carriage bolt fits into the toggle switch slot in the cover and this keeps the bolt from turning when the post is twisted. I used 6 inch carriage bolts so I could adjust the height of each post by plus and minus about 2 to 2.5 inches.
And here is the FAILED part, and an alert to you of something to watch out for. This structure is "floppy"... the posts are just sitting on the concrete blocks and can easily tip slightly off of plumb. They are also not attached rigidly at the top end, so that can easily flex to allow the whole structure to "LEAN" in any AND ALL directions.
You will probably fair better because I assume you are intending to make rigid attachment of the stringers from post to post. This will definitely improve the rigidity, but unless you have some longer triangular supports (gussets), the taller the post the more leverage against that rigidity there will be. I also would recommend that each support point be two posts (instead of the 2-1-2-1-2-1 system I used) as this will also improve the rigidity of the whole thing.
I recommend cross bracing at every pair of support posts and some cross bracing from one support point to the next at a minimum of every three sections along the length of the line.
I think the "post spikes" you are proposing to use will work well if the rest of the structure is rigid enough.
Another point I might bring up. I tried to get by CHEAP, (regardless of the silliness of purchasing 60 landscape spikes, 60 t-nuts, 60-carriage bolts and 60-metal light switch covers!) and made the base for the track just a 1x6 board on 1x4 stringers. This meant I needed more support points in the curved sections to allow the curved track to still remain on the straight boards from support point to support point (fitting a curve to a polygon of straight sides). I strongly recommend that you make the whole raised structure at least 18-in. to 2-ft wide along the whole length. I have a YouTube video that will graphically explain why I feel that way!