What is the ideal?

Id suggest splitting it as per the rough numbers on the attached, it will take work and you must meet all conditions (including more not outlined, please check first) but this is what will make you the most money outside of a H2B ISA or a LISA as we assume will be available next year.

If you do want a Help to Buy ISA then Barclays pay the best bank interest rate on top of the governments 25% mortgage voucher at 2.27% but while you wait to fill it you might as well open the accounts Ive listed so that the bulk of your money is earning interest alongside it.

Thanks Jennie,

I wondered if I could open an H2B Isa, but would it matter if I later decided not to buy a house? Or can I only use the interest to help buy a house when I have enough saved?
If you decide not to use the money for a for your first house deposit then you only profit from the bank's interest rate (Barclays as an example would be 2.26%) and do not collect the 25% voucher from the government (via your solicitor). Therefore it makes more sense to save it in a current account or a monthly saver which bank vs bank have a higher interest rate in cash terms.

Also a query about some of the accounts require a payment of £1000 per month, but they expect you to save no more than £2500 savings in that account; how does that work if you wont use that account for having wages paid in (as it would go past 2500 fast). So would you need to maintain a limit of £2500, by transferring £1000 every month to that account and then moving money out to make sure it doesnt go over £2500?
Apologies for this sounding confusing, but the process does seem like it.
Yeah it is confusing initially because they don't want too many of us profiting from it so you can go over the max but won't get the good interest rate on the extra amount. What I do, because I've set it up for any new savings to only benefit my H2B ISA, is everything pays into each other at the qualifier amounts needed on one day and then the next day they each pay the other back the same amount. It's easiest for you to do it all on the same day and take the highest value so all the transactions cancel each other out in one go and it isn't as confusing; For example if you need £500 in A to get the interest, £750 in B and £1000 in C, on one day set up a monthly standing order so account A pays B £1000, B pays C £1000 and C pays A £1000. It doesn't matter how much you have in each as long as they meet the monthly amount you've set up (£1000 in this case). And if you find any exceed the level where you get the good interest rate you don't get penalised by the banks, you just aren't using the extra money effectively because you could open another new account with a good interest rate on it. If you do expect to save more than your £17k I would add in Santander or if it's a minimal monthly amount (usually £25-£250) my preference would be a higher rate monthly saver but that's with harsher rules as it locks you in for a year before you get given your interest on it.

Thanks x

I hope you find this edited quote makes sense of it all but let me know if you need anything else. Like I said, grabbing a switching bonus would be great too, but I know I've thrown a lot at you already.

Thanks Jennie, that helped so much !