I'd advise against using tape in only certain spots. Tape may seem thin, but it doesn't take a lot of height difference to mess up a first layer. I usually use a piece of paper to set the height of my first layer, and most tape isn't much if any thinner than a piece of paper. So you're talking about creating enough variation in the base to account for the clearance usually left.
I second that aquanet RB posted, I bought one can a few days after getting my printer and two years later it still feels like I haven't used any. I use three coats on a fresh sheet of glass. I put them on very light and give them a minute or two to "cure" before putting on the next one alternating the direction I spray (First layer I spray vertically, second horizontally, third vertically again.) I actually use mirror tiles instead of normal glass...because I have a bunch of them on hand. When sprayed I can still see reflections in the mirror but they look a little hazy.
If I'm doing big critical prints (like when I printed my MPCNC) I put on a light top-up coat each print. But for day to day use I only top it up when things stop adhering well or when I notice it starting to get thin (shiny spots showing through) or dirty (from dust and such collecting.)
When it gets dirty or thin I clean it off with windex or rubbing alcohol then do a fresh three coats.
That test print looks like you've got some serious underextrusion going on as Litterbug mentioned. Could be a number of things. Clogged nozzle, too cold, bad settings, filament slipping in the extruder (loose idler), gear on the stepper in the extruder slipping on the stepper shaft (really common on some machines - especially if the stepper shaft doesn't have a flat so the set screw is all that keeps the gear from rotating.)
I'd start by checking the mechanics of the extruder - make sure the drive gear is tight and the idler is creating enough tension.
Then I'd so some calibration tests.
First check is that your extruder steps are correct, here's a blog with details on how to do this:
https://northwoods3d.weebly.com/blog/filament-calibration-part-1
But the short version is you make a mark on your filament 100mm above the extruder then tell the printer to extrude 100mm (you'll need the hot end heated up) The mark should now be at the top of the extruder. Since you're underextruding it will probably not go that far but instead be somewhat above the mark. So you can measure the difference and adjust a firmware setting on your printer to correct. Wash/rinse/repeat until you get 100mm of filament extruding when you tell it to extrude 100mm.
The next step is why I don't like Cura. It won't slice single wall prints and deals with perimeters differently. So instead of using a print with a known thickness wall you have to slice a solid cube and tell it to print it with just one perimeter and no top to do this. But basically you want to confirm that you're getting extrusion of the correct width. In general you'll want your extrusion to be 120% larger than your nozzle so with a common 0.4mm nozzle you'll expect your extrusion to be 0.48mm thick. So the basic idea is to print something with just one thickness of extrusion and measure it to confirm you're actually getting 0.48mm. If not you then adjust your extrusion multiplier and repeat until it is. Here's another article from that same blog explaining it in more detail:
https://northwoods3d.weebly.com/blog/-flow-rate-how-much-plastic-is-coming-out
That second step is optional unless you really want accurate parts. For me...accuracy is important so I do it for every new filament and setup a custom profile in slic3r for each filament.