To help you tune up I have provided a number of tuning note tracks here. I use A=440Hz as the default tuning on my website.
Most of my tracks start with 2 seconds of silence at the beginning and end with 4 seconds at the end.
However, it is quite easy to add more silence between the tracks, by adding 'silence' tracks to your playlist. This can be especially useful if you are playing many pieces back to back and want more space between the movements.
Here are some silent tracks that you can use.
Another option is to use an audio editor such as Audacity to insert a specified length of silence at the start or finish. The advantage with an audio editor is that you can also use it to add silence in the middle of a track, for example if you want more time to play a cadenza or need a pause somewhere. Audacity has it's own 'generate silence' option which can be found in the menu options.
Many of the works on my website correspond to scores that can be found on IMSLP. So long as you adhere to the copyright rules relevant to your country, you may download and practice from the scores on the site.