Hi,

1) If I use Syslog-NG with a flat text file to receive 5000-6000
logs/sec, using s fast disk from my storage, do you recommneded to me
this option ???

The file destination of syslog-ng is capable of handling 5000-6000 logs/sec. But if you have problems, you can open an issue on Github.

2) As an extra benefit, what is the best and simple way to have a
graphical view of all the logs ???

AFAIK there are no tools for visualizing logs in case of file destination. However, if logs could be forwarded using ElasticSearch destination, Kibana could be used to visualize logs. Also, if you configure a mongodb destination, you can use mojology (https://github.com/algernon/mojology).