How much of my portfolio should I consider putting into riskier investment assets such as P2P lending?

P2P in Singapore, while better regulated, still has its fair share of risks.

You should probably look into other stocks, REITS, ETC before P2P if your goal is diversification.

If you have done all that and still would like to try P2P but are unsure, then probably start with what you're willing to lose to test the waters and see how that goes.

From the research I done P2P lending is never a good choice... I watched videos about it and ultimately it doesn't really work out well. Unless you're lucky, read their T&C before investing. Know how they conduct checks / requirements for people who are looking for loan or how they use your money to make more money.