Multi-currency checkout + free shipping conditions

[CK3]

Hi guys

So I am facing 2 problems here. My default store currency is in SGD and I would like to sell internationally.

(1) I am using the Best Currency Converter app and it works fine. So in terms of viewing prices in their home currencies, my customers are seeing $xx.99 and not some strange $××.27. I have gone into Shopify settings to add payment regions, and when I click on "edit", I can view (but can't change as I am on the $29/month plan) rounding up condition for each country. However, Shopify does not allow me to click on the "save" button at the rightmost bottom of the page. When i try to checkout, the default checkout currency is still in sgd. What should I do to change the checkout currency to the home currency of the customer so that the there checkout process is seamless? I have already enabled sholify payments.

(2) Once I resolve the above issue, i have another problem. I currently offer free shipping to customers who order sgd150 and above. Once my customers start checking out in different currencies, how do I extend the same offer to international customers in their home currency? One alternative is to offer free shipping to customers who order 2 items and above. I went to Shopify shipping settings but the only 2 conditions they offer are item weight and price. There is no condition set for item quantity. 

Thank you.