theratypist

Yes, your rating is the average of all your ratings... So the more 5 stars you get in the future, it will improve your average rating. Also 4 stars is not the end of the world 🙂 But I can see how its an important metric here on Fiverr...

People who are the best at their niche will get an order, if they didn't then they wouldn't be considered the best.

No, you can't send zoom links. Only use the video button that's available on Fiverr. 
https://www.fiverr.com/support/articles/360011062838-Video-calls
Zoom video call capabilities by user
Fiverr is currently beta testing this feature and it is not available to everyone at this time. Please stay tuned for updates.
Fiverr Business  
Sellers can initiate a video call, before or after placing an order, from either the inbox or Order page.
 
A seller with a Fiverr Select buyer
Sellers can initiate a video call, before or after placing an order, from either the inbox or Order page.
 
PRO sellers
Pro sellers can initiate a video call after placing an order from the Order page. 
 
Gig workflow
Orders created from the Gig workflow have access to Video Calls. 
 
Other sellers
If you're a seller with a Gig in one of the sub-categories below, you can initiate a video call from the Order page:
App Design Architecture & Interior Design Astrology & Psychics Book & eBook Writing Business Consulting Cooking Lessons Craft Lessons Customer Care Dance Lessons Financial Consulting Fitness Lessons Game development Gaming Industrial & Product Design Legal Consulting Life Coaching Marketing Strategy Mobile Apps Online Coding Lessons Online Language Lessons Online Lessons Online Music Lessons Scriptwriting Songwriters QA & Review Web Programming Website Design WordPress

Only orders that start at a total of $100 can use milestones, hence why you can't price anything under $50, because the least that can be done are 2 milestones at $50 each that total $100
You can read more here: https://www.fiverr.com/support/articles/4414438601873-Milestones?segment=buyer
The most you can do is just treat them as separate orders (they are practically the same thing - cost wise to the buyer).

That's a tricky question! But here's the exact answer, you can discern from there what you take from it. Hahaha when in doubt, you can clarify with Customer Support -- support@fiverr.com
https://www.fiverr.com/support/articles/360017173498-Subscriptions
You can cancel a subscription order and it won’t affect your seller metrics—go to the Order page > Subscriptions tab.
You must cancel a subscription at least 10 days before the renewal date so that your metrics are not affected Your metrics are only affected if you cancel after an order that has already started

If you have no levels as a seller / new seller you only get to see a limited amount of buyer requests. A buyer request gets removed from your view once 10 other no level seller / new seller has made an offer on that specific request. So, the buyer request is kind of a matter of making the first offer once it appears. 
Once you get to Level 1 and up, you will be able to see more buyer requests and it will not be removed from your view anymore.

Yes, I would agree with this just go with the cancellation. You haven't worked on the order and buyer has already informed you that they purchased from someone else. I don't think you'd want to waste your energy for someone not interested in getting your output anymore. Plus forcibly delivering something will just waste your precious time working on something that could potentially get cancelled (either through CS or even a chargeback)
Well, I don't know what the weight between a cancellation vs. a bad rating in terms of how it affects gig placement. But a bad rating can happen both privately and publicly (the buyer can rate twice).
Also as I mentioned earlier, the cancellation might not even affect your completion rate if CS assists you. And if it did, it would get back to 100% after 60 days. If you get a bad rating of 1 or 2 stars, you might not even be able to bid anymore in the buyers requests and that's usually something helpful for new sellers to gain more momentum. Add-on to whatever the buyer may have written on your review.
Totally not worth your time and energy. You are a new seller, whether we like it or not, good ratings matter a lot in that stage. It helps potential buyers take a decision with us more than a cancellation rate that cannot be seen and resets eventually after 60 days.