Also, to add to what phil mentioned above:
When transferring money around between ISA’s, always do it via ISA Transfer Forms, and not via a normal bank transfer, otherwise the money will lose it’s ISA status.
In any one tax year you can pay money into any type of ISA, providing it is not of the same type in any one tax year.
So you could put 10k in a S&S ISA and 10k into a cash ISA.
What you CANNOT do though, is put 10k in a S&S ISA, then open up a new S&S ISA with another provider in that same tax year and pay the remaining 10k in.
Also, you can only pay in 20k per tax year, regardless of what type of ISA you put your money in.
Any profits made in a S&S ISA can be reinvested, no issue there, it’s free money from then on Reinvest to your hearts content.
The awkwardness of ISA’s only really apply when taking money out of the ISA wrapper or putting money into an ISA. Always use ISA transfer forms if transferring from an existing ISA. If paying money in from a normal savings account, then you can use card etc no problem.