There are three ways to drain this unit. Please see the manual that is downloadable from this product page to determine the best method of draining for your specific application.
Based on a 1 GPM kitchen faucet, the water will remain hot for approximately 2 minutes before noticing a temperature drop.
This unit has been replaced with Model # ES 4 Internet #206393135. https://www.homedepot.com/p/N-4-Gal-2-Year-Mini-Tank-Electric-Water-Heater-ES-4/206393135 Neither unit had /has a drain plug. In the "Info & Guides" Section of the ES4 listing, select "Use & Care Manual" and got to Section 5.2 "Draining the Heater" to review three differnt methods of draining the unit.
I think you spelled "Ariston" and you were auto corrected to "artist". These units allow you to set from Low through High. The temperature will set between 65F and 145F. First, turn the unit to High (if not already done). If this does not work, the most likely issue is a defective heating element. This part can be replaced. Corrosion from minerals in the water can damage the heating element. This is common to any tank reservoir water heater and is more common with the greater hardness of water used. Hardness refers to the level of minerals in the water and varies by geography and municipality.
The reset button is underneath the front cover. You should disconnect the power before accessing the reset.
This unit should NOT be side mounted. This unit is designed to be installed vertically. The connections may connect using a flexible connection that can allow for the incoming and outgoing lines to initiate from other than above the unit. For the pressure relief valve, take care to follow the manual's instructions regarding its line's amount of drop from the valve.
From my experience with this water heater I would think it would work just fine to provide hot water to two sinks.
Somehow you have found a dead product page. I have advised THD. In the THD.com search bar, type in "Bosch ES 4" (do put a space between the S and the 4). This will take you to the active product page. I'm with Bosch and cannot quote pricing or you stor's local availability.
I am using mine under the counter in a "yurt". It was simple to just insert in the not water line and plug in to a regular outlet. If you have the room? I would think it would be a great addition for a travel trailer.