Welcome onboard Iain.
You have it more or less correct.
Each summit you activate and qualify (minimum of 4 contacts for qualification) scores the points assigned to that summit; in your case last year, 4+1. Some of the higher summits during the winter period (Dec- Mar) also attract a winter bonus of 3 points (your 4 pointer would have scored 7 points had you not done it in the summer!).
You can only claim points for a summit once per calendar year.
S2S is a chaser award and is unrelated to qualification to MG.
You just happen to be chasing other activators from a summit. It has it's own individual award.
You can accumulate points from the same summit on a daily basis (see rules for clarification).
Yes, living in Norfolk means a lot of travel.
In my first year of activating I managed to accumulate 11 points in total so understand where you are coming from.
I decided in year 2 to travel long distances, especially during the winter months to improve my scoring rate. After 3 years I'm now sitting with 400 points and the long term goal of MG is at least 3 years away.
Yes, there is a huge disparity between Shack sloth and MG.
I acquired (without any real effort) SS within 6 months. Many have done it in a few weeks.
MG takes real work and dedication and, unless you're lucky to live in an area with a huge number of closely packed 10 pointers (that's a different thread ) , then it can take years to reach the goal.
Be warned it is addictive and you'll walk in some fantastic countryside which you'd probably never have considered before
Have fun and keep asking questions.