Can someone please help advise on this?

So if I have taken up this Flexi loan, say RM200k, and within the next few months re-paid in full amount. That would leave ~RM200k balance that I'm free to withdrawn, plus no interest chargeable.

The questions are:
1) How does the monthly installments work then? Is it still needed to pay every month? That will bring the account to a positive value, with the extra amount not interest payable (as compared to putting it in FD).

2) If the loan tenure is for 30 years. Any problem to just leave the amount there for like 10 years? Lock in period before redeem title is 5 years.

Actually with just RM3k in the a/c, it's already enough to contra the rm10 monthly charge (assuming current BLR-2.3). Do bear in mind the interest saved is calculated daily. Any amount stays in the a/c (eg. your direct auto-credit salary) will help reduce the interest. In long term, this is something you won't notice. It worked in my case
Of course one can opt for semi-flexi loan but for each withdrawal, bank will charge u RM25 and also 2-3 days notice is required prior to the withdrawal. I will go for full flexi loan for the 1st housing loan. If u have 2nd or 3rd loan, then it would not make much sense to have the same loan type for the subsequent ones.