Andrea, your assumptions all look correct to me. Don't forget also that if you sell shares at a loss, you can carry the loss forward into future years if you've insufficient profits to write it off against in the current year.
The Oct 31 deadline is for tax payable on share gains between Jan 1 and Sept 30 of that year. CGT on disposals in Oct-Dec are payable by January 31 of the following year.
Costs and fees associated with acquiring and disposing of shares are generally deductible against profit, yes.