JR Shikoku Rail Pass v full fare?

Thank you in advance forum users,
I am trying hard to work up a 1 mth itinerary for our first trip to Shikoku. We will be arriving via Brisbane-Narita-Matsuyama in April 2020. We have the time to linger and not rush around Shikoku, so we are planning to spend a few nights on Shadoshima, and 2 nights on one of the islands while riding the Shimanami Kaido. The rest of the time we want to avoid staying 1 night anywhere. We also understand hiring a car seems unavoidable, otherwise we LOVE using the rail/bus system. This being the case, I am coming to the conclusion that the JR Shikoku Rail Pass is designed for people who need to cover a lot of distance in a short time...people who need to cram their travel on Shikoku into 3, 4, 5 or 7 days. Am I right in presuming that I have the choice of deciding on short, sharp bursts of distance covering while squeezing every cent of value out of a JR Shikoku Rail Pass versus doing things in our time and paying a full fare? This is my first question. Secondly, Google Maps for example calculates Matsuyama Station to Imabari Station at Y2,220 (Limited Express) and Y950, while the Maps on my Mac PC calculates the fare at Y1470. I'm confused! I need to know how to accurately calculate the cost of rail/bus travel in the planning stages and while on the ground in Shikoku so I can decide on buying the Rail Pass or just paying full fare. So which trip planning app is best for fare accuracy?? Thanks again in advance for your help. Japan-Guide is absolutely indispensable. I have worn out all Shikoku related information on this website.

Use hyperdia to calculate fares.

Wow! HyperDia is amazing. Never used it before. Thanks so much...it looks good

Hyperdia is amazing. Just note that the total cost of the ticket is shown next to each Route. The column labelled Fare does not include any seat fee.

Used hyperdia and it will solve all your questions! Really need to decide what you want to see

HyperDia is never designed to check whether a rail pass pays off.

Personally I think HyperDia is relatively not recommendable;
I know it has some problems which can cause travelers to be confused or mislead.

We will be arriving via Brisbane-Narita-Matsuyama in April 2020

It is too early to use a route-finding tool (like HyperDia and Jorudan)
for actual railway costs and train time regarding your trips (#1) (#2).

How will you come to Matsuyama? By a direct domestic flight from Narita?

I need to know how to accurately calculate the cost of rail/bus travel in the planning stages

To calculate (nearly) correctly your JR regular cost,
you need to know some JR rules about the basic fare and the service surcharges.

It seems there is a common misconception
to think as if your total JR cost were always found by adding up a JR cost for each leg,
which may lead to a wrong conclusion that a rail pass pays off while actually it is too expensive.

The amount of the JR basic fare per unit distance
generally gets lower as the distance gets longer.
You can pay the basic fare for a whole JR route where you neither turn back,
which should be completed when you return to any station which you already left.
The length of the validity period of a JR basic-fare ticket is decided basically by the distance.

So,
your total JR cost can vary
by how you set a route for one JR basic-fare ticket to correspond to,
and that depends on your itinerary and timeline.

For JR conventional (= non-Shinkansen) Limited Express surcharges,
there are a few rules to give a 50 percent discount when the specific requirements are met.

(#1) From October 2019, the rates of Japanese national and local consumption taxes will be raised.

(#2) In March, JR regional railway companies may revise their train timetables.

"You can pay the basic fare for a whole JR route where you neither turn back,
which should be completed when you return to any station which you already left. "
-->>
"You can pay the basic fare for a whole JR route, on the following three conditions.
: You do not turn back.
: You do not skip any part of the route.
: When you return to any station which you already left, the route should be completed."

Sometimes that is more complicated to understand and actually implement. Most people want a general idea of what individual trips will cost and then add them up to see if a pass pays off. If the pass is 19,000yen, for example, and the trips add up to 45,000yen, then sure, go for the pass. If the person is a penny-pincher and needs to save every single yen they can, well, a point to point ticket with tstops along the way may be the way to go. Another thing is, while Hyperdia doesn't update the exact times until the revision has happened, one can still look at the times and schedules to get an idea of the frequency of a service. The revision may be a difference of a few minutes at most (for the most part). As the time draws nearer, one can re-check to see what it will actually be (the schedule). I look at Hyperdia now for November just to get an idea of what I want to do. I would suggest others do that as well, since it's just a general idea of what is available.

Most rail passes require longer distances for them to pay off, for something like Takamatsu to Matsuyama being only 6,190 yen on the limited express implies you need to do a couple of those journeys within seven days to make a pass pay-off.
If you are wanting a slower paced trip, then it will probably be the case that the pass doesn't offer the savings you need.
Hyperdia is a good tool for an indication of costs, and the fine adjustments mentioned above about through trains/multi-stop journeys should/would not be enough to make a difference in choosing a pass over single tickets. It should obviously save you a decent amount of money (several thousand yen), or not. If not or even marginal, then you might not bother. Sometimes the rail passes are more bother than a minor saving.
A related point, the pass does provide other discounts, although they might not be very large - your ferry to Shodoshima for example.

In Shikoku, highway bus is cheaper and often faster than railway because the island doesn�ft have shinkansen but has highway network from north(Takamatsu) to south(Kochi) and from east(Tokushima) to weat(Matsuyama).
For example, it takes 2h 30m and costs 3600 yen from Matsuyama to Kochi by bus.

http://www.jr-shikoku.co.jp/bus/global/en/
https://www.kosokubus.com/en/