@Piers24 Ok so lets try and give some suggestions:
1) You need to create a ruleset(s). You will definitely need one that you could call PEAK. This should have a minimum of 7 nights stay with check in/out only allowed on a Friday. You then highlight the dates you want this apply to in your multi calendar and click on add ruleset somewhere on the right hand side. This will allow people to book a fortnight as well.
2) Your listings should have a min stay of 2 nights (we use 3 by the way) and a max of 30 nights if you want to ensure you meet the Furnished Holiday Let tax rules. That said you are not available to host for 220 days per year so this is maybe less relevant. You could make the properties available for longer but at such a high price (in April/October that no one would book (I think that is legal!)
In the pricing section of your listings you should set a base price for each. Its under the smart pricing section and even if you have smart pricing switched off this base price will be used as you open up your calendar. Set this price to the highest you would ever want and then if you miss your calendar opening up then your price will at least be nice and high.
Let us know how you get on. Feel free to tag me by typing @ and then clicking on my name.