Hey Lewis 
As @Racxie kindly suggested, you can find more information about the crowdfunding here. The limit per individual is £25,000, down from £50,000 in R4.
R4 has already concluded, the next one in June is going to be R5 
Whilst it is indeed £25,000 you need to qualify for Alpha for life, it was the same in R4, whereas only £5,000 in R3 and £1,000 in R1/2. I doubt that Freetrade expects its investors to attach a monetary value to the perks - they are just minor augmented benefits to the core offering - a stake in the company. Whilst it may seem excessive to grow in multiples of five in between the rounds, it is, after all, meaningless in case of Freetrade’s failure and relatively insignificant in case of its long-term success 
Alpha does not, in fact, exist yet, so we can only speculate what it could offer - free transactions, instant top ups, unlimited Apple Pay, multicurrency accounts, you name it. Hopefully, there will be more clarity on it next quarter.