Remarketing

I have almost 116.7k traffic on my website. Majority of the traffic is coming from Organic.
I want to know how do I do re-marketing. I have some lists but I believe these lists are not being used effectively.

I would like some expert and serious opinion or a resource material. I want to do it by myself and not want to hire any agency at the moment.

Google Tag Manager Issue

Something weird is happening. Sometimes, Google Tag Assistant shows that my tags are actually working fine.
The very next day, it will start saying that there’s no tag attached.
Moreover, sometimes it will show one analytic code while sometimes, it will show two analytics.

Is there anyone who can help me that what’s going on actually.

A/B Testing

I am running two ad campaigns at the same time by allocating different budgets.

A: 10$ per ay and getting 236,477 impressions against 80$ so far. while I got 8086 views only. My CPV is set to
0.01 and view rate is 3.42%

B: 20$ per day and got 130,365 views so far by spending $40.49 while got 5307 view with the view rate 4.07%

Which one is fine and what more I should do to yield some good results?