<p>I've built and done some simple tests on a TEVO Tarantula but I've noticed some pretty dramatic under extrusions. </p>

<p>My equipment:</p>

<ul>
<li>TEVO Tarantula;</li>
<li>Jim Brown's easy config fork of Marlin;</li>
<li>Titan extruder (came with printer).</li>
</ul>

<p>I've updated the firmware with the 400 steps as advised and calibrated the extrusion with the 100&nbsp;mm method:</p>

<ul>
<li>When I run the calibration with the Titan extruder, <em>only</em> the 400 steps is fine and works as expected;</li>
<li>When I connect the Bowden tube to the hotend and calibrate (at 200, 225 and 250°C), I see only ~50&nbsp;mm of extrusion. </li>
</ul>

<p>I've disassemble the hot end, changed filament and I can't see any signs of blockage. The Bowden tube in the hotend is not showing any signs of melting etc. and it is pushed all the way down to the hotend, as per the instructions. </p>

<p>So, what's going with this?</p>

It is considered good practice to limit your post to one question at a time. The question about hardware and material is too broad to be a good question and I will set that aside.
Equally unfortunate, your drawing is ambiguous. I suppose if English is not your native language, I'm not helping things either.
The drawing has some errors that make it challenging to be certain of a correct answer, but I can provide you with some useful information as a direct result of a test print created today.
The test print for my printer creates a series of spool shapes within retainer shapes. More complex than a simply cylinder making the test that much more difficult.
My printer is able to print without problem parts that are 1.0 mm apart, 0.8 mm apart and 0.6 mm apart. The test failed at the 0.4 mm spacing and the 0.3 mm spacing, telling me that I need to perform some tuning.
Your question asks about 0.05 mm spacing. I think you will not find an FDM  printer that will manage such separation without bonding together the individual components. FDM printers use filament.
You may also not find that an SLA or DLP printer can provide such tight tolerances. It is the most likely source of a success, however. I have only minimal exposure to tolerance in this type of printer. SLA/DLP printers use lasers/light and liquid resin. They can accomplish 0.05 mm layer thickness, even as small as 0.025 mm layers, but I do not know the figures for horizontal precision/accuracy/tolerance.
SLS printers use a nylon powder and a laser to fuse the powder together to form the model. My SLS printer uses 0.050 mm powder. To accomplish the separation you require would mean a single layer of powder will separate the individual segments of the model. This is not practical for this type of printer.
Your best bet would be to consult with a 3D printing service that uses SLA printers. SLA is likely to be more precise than DLP due to the method of exposing the resin, although that is not a universal truth.