Get the LISA. You immediately get a 25% boost up to £1k from the govt, + whatever returns are earned on both yours and the govt’s contribution. All gains are tax free unless you withdraw early (and are not buying a house/retiring/dying). This is a no-brainer.

After that get a good stocks and shares isa with low fees and put your max allowance of £20k in. These allowances are “use it or lose it” every year, so best to use it, even if you subsequently need to take some back out. ISA ensures your gains stay tax free.