High RAM leading to High Battery consumption

Your computer performs best when connected to AC power. It can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, the charged state may even decline during stressful work.

When used only on battery, your computer has no extra cushion of power, and will perform more slowly. However, for ordinary non-stressful tasks this may not be objectionable (possibly not even noticeable.)

In general, you should ALWAYS connect AC power when it is possible to do so, and only run on batteries (which will be somewhat slower) when no AC sources are at hand. There are three micro-controllers cooperating on battery and charging issues, and your Mac will NEVER over-charge.

A charge cycle is ever-so-slightly destructive to batter longevity. When operating as designed and not using Battery Health Management, battery charge level is allowed to decline to about 92 precent level before initiating a recharge cycle to top up to about 99 percent.

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The latest Catalina software update for MacBook Pro with T2 chip (2016 models and later) includes a new feature called Battery Health Management. Based on you usage patterns, this widens the hysteresis to initiate a charge cycle a lower level, and stop before 99 percent.

About battery health management in Mac notebooks - Apple Support

This relaxes the set points around re-charging (based on your usage patterns) and can improve long term battery lifetimes. When active, recharging may stop short of 100 percent charged.

The important metric is memory pressure. Yours graph is very low and all green. You are fine, and this will NOT cause battery problems.

"Unused RAM is wasted RAM"

CleanMyMac and its ilk will slow down your Mac, because those cached files may be referenced again, and there they are, in RAM.

When your Mac needs more RAM for other things, those cached files will be removed based on least-recently-used, and that RAM will be made available in a heartbeat.

No. These are routinely NOT installed on new Macs, but new Macs are eligible for purchase for $0.

Once you create an Apple-ID, and log in to the Mac App Store with it, your purchases are yours.

You should be able to "Purchase" those Apps at no cost to you.

Try it -- and report if anything other than complete success, noting the EXACT wording of any error messages.

The original item, shipped on your Mac, would be tied to the Mac serial number or one of Apple's own Apple-ID. That is why you could not update it, but needed to replace it with your own (tagged with YOUR Apple-ID) copy.

The fact that it is using 7GB is not in itself a problem. Modern Macs are designed to use as much RAM as it needs. To check what may be causing excess battery drain, check the CPU usage percentage.