Understand Tracer parameters

[GretaRom]

Dear all,

Could you help me with ESS problem?

I used Beast 1.10.4 to analyze 100 Echovirus sequences. 

I am new to phylogenetic analysis but I read all beast tutorials. However I still don't understand which parameters must have ESS>200 and which should have ESS>200.

Here you can see my runs. The sequences were analyzed with GTR+G+I (derived from MEGA): 

-10^8 chain and log every 10^4 with uncorrelated lognormal relaxed clock  and coalescent costant tree prior (96.log)

-10^8 chain and log every 10^4 with strict clock and coalescent constant tree prior (parsedStrict.log)

So, some parameters are good and others not at all. 

1)Can you explain to me which run should I consider valid and which parameters should I consider as essential for ESS value (also for future analysis)?

2)Should I run again the analysis using a longer chain?

3) What is the Burn-in parameter and why is so important?

4) Do you think that my molecular clock setting are suitable?

THANK YOU SO MUCH

Greta

PS: If you have books or article to better understand these parameters will help. Thank you