My plan is to arrive UK on Mar 2020 via a Tier1E Visa.
When I check on the GOV website, it states "The earliest you can apply is 3 months before you travel." and "You should get a decision on your visa within 3 weeks."
However, when I come across with the post regarding processing time in this forum, I find it is quite often the processing time took more than half year!
So, I am a bit confused on when should I hand in my application if I am intended to arrive on Mar 2020.
The second question is I was on Tier5 visa from 2015-2017, will home office check my previous immigration record?
During those two years, I "worked" for a travel company as a tour helper while they provided me with hotels, meals, attraction tickets and some "pocket money", which was not up to income tax/NI threshold. Therefore, I did not make any contribution to either income tax or NI and I did not claim myself as self-employed to HMRC, as I did not know I have to.
Will my Tier1 application be affected? I am not intended to any tax fraud

My plan is to run a luxury tour operator based on my experience previously.
Thanks in advance.