There are a number of physical formats you can consider when buying platinum:
When investing in any asset, including platinum, it's important to keep the time horizon in mind. Prices fluctuate, and over a longer time horizon there's a better chance of your investment appreciating in value.
The last thing anyone would want is to invest money they'll need in the coming months, only to have the market move against them. Talk to your financial adviser, and carefully plan any future purchases.
As a general rule, you should look at buying legal tender platinum coins wherever possible. This will almost certainly include less overhead and premium than other formats, and be closer to the true spot price of platinum.
Purchasing rare platinum coins should be avoided unless you really know what you're doing. Some subjective measures of value are easy to misjudge, and may result in you getting taken advantage of.
Having liquid platinum on-hand and ready in the event of a crisis is the best hedge. Being invested in platinum ETFs is fine depending on your objectives, but if you're truly hedging against unforeseen market collapses, you want physical metal in your possession.
Buying platinum on credit or speculating on the future price can lead to getting yourself in a significant financial jam.
Instead, put some money to the side that you're sure you're not going to need in a short time horizon, and use that to invest.