Is it always necessary to carbonate your beer with sugar or tablets or is it possible to get the right amount of carbonation with the primary and secondary fermentation?
In short, no, not if you're using an airlock. You need pressure to reach the levels of carbonation required. With an airlock, you only get atmospheric pressure, so the pressure inside is the same outside.
Carbonation is measured in volumes of CO2. 1 Volume of CO2 is the same volume of CO2 as beer - 2 volumes would be twice the volume of CO2 as beer at atmospheric pressure.
At atmospheric pressure, fermenting with an airlock, you get about 1 volume of CO2 dissolved, yet common beer styles require 2.0 or more volumes to be considered carbonated - 2.4 vols is a common figure. To get more than 1 volume you need pressure. This is why carbonation is normally done in the bottle or keg where the required pressure can be maintained.
If you were fermenting in a pressure-capable vessel, such as a keg, then you can pressurize the CO2 produced during fermentation. You use a spunding valve and crank up the pressure towards the end of primary to increase the pressure inside the keg to the required level for carbonation - 12-15psi is common.
You could do without priming, it's just not practicable. If you have a quick fermentation sample and know what the final gravity will be, you can check on the fermenter every couple of hours and when the gravity gets close enough to the FG, you bottle. In German, this is called
In real life, your need for sleep, a day job, social interactions, and such will probably make this difficult.
Actually you can. You just need to know the final gravity of your beer. This could be done by attenuation limit test (you take sample of your beer and add good amount of fresh yeast and let it ferment quicker by shaking, keeping in top region of fermenting temperature) see instructions here: http://www.brewwithfermentis.com/2010/11/29/attenuation-limit/ just shake it as frequently as possible and keep it in good temperature and you should get your result quickly. Then you measure SG of your fermenting beer (it is slowing down when it is reaching FG). You could even slow it down by lowering the temperature to the low regions of fermenting temperature (ie. if you are not sure you will be around). Once your desired gravity is reached, crash cool to 7 deg C (for Ales) and leave it for few days to settle. Then bottle/rack and leave bottles/casks in room temperature for few days, yeast will "wake up" and ferment residual sugar and create natural cask condition. General rule of thumb is botttle/rack when SG reaches 2-4 points above attenuation limit. Precise calculators could be found on internet. Temperature control is a must, but you can just get any old freezer and temperature control device from eBay - with this you can keep any temperature you want (21 deg C, 7 deg C whatever) in your freezer, both will cost you less than 60 quid and you will be able to produce much better beers.