Premium memberships have more ads than free (Standard) membership. Also, you will earn only 40% of the earning of your referral clicks while with a premium membership you will get 80%-100%. But if you upgrade at the beginning, your clicks are not enough to cover the membership cost. So, begin with a free membership, collect direct referrals and when you have some active referrals, upgrade. You may have unlimited number of direct referrals even with the free membership.
Both the free and premium members have to click at least 4 ads daily in order to earn from their referrals. So, if you have referrals, do not forget to click daily (according to the server time).
If you want to click the most number of ads, try to click just after resetting the server time (when a new date is started on the server). The server time will be displayed at the bottom bar when you have logged in.
ScarletClicks is my favorite site for renting referrals. The average is good and stable. But don't just rely on me blindly and go to their forum to study other people's statistics. Do your homework and decide yourself. The rental fee varies according to the total number of referrals you have. Checkout the FAQ page to know details about the rental costs.
You are not required to invest in order to cashout. But if you do, the only restriction is that your payment processor must be verified. Which means, you cannot invest from an unverified Paypal or Payza.
Another loving feature of ScarletClicks is, you can invest from one processor and withdraw another processor. For example, you can add money from Payza and withdraw money to your Paypal account.