UK taxes and cryptocurrencies

I live and work in the UK. I work at the company, so my employer handles the income tax. I also own some stocks but I keep them in stocks and shares ISA, so I don’t have to pay tax on them. Now let’s imagine that I start trading cryptocurrencies. As far as I understand, I’ll have to pay Capital Gains Tax if my total gains on selling cryptocurrencies exceed £12,300.

• If my gains do not exceed tax free allowance, do I still need to report anything to HMRC?
• Do I understand correctly that if I own two cryptoassets, and I sold one of them for profit of £13,000 but another one for loss of £1,000 within the same financial year, I should calculate my total gains as £13,000 – £1,000 = £12,000, and therefore I am not subject to the Capital Gains Tax?
• When thinking about the gains on cryptocurrencies, I don’t have to think about the gains on stocks that I keep within an ISA, right?

Thank you.