If $500 returned $10k in 18 months, would that be a good return or is it too good to be true....
Let's start with this, it's possible but not all that likely. There will be many who have achieved that but you'd have to hold a fairly risky portfolio, it's unlikely if you hold major coins like bitcoin/eth.
What would you consider a reasonable return on your investment after 12 to 18 months (your investment is locked for 18 months with no access to it)? Minimum investment would be $500...
Anything greater than 0 is reasonable. Over 18 months I would personally aim for about a 5x return. As I said above, more is possible and as is less. The more risk averse you are the less likely you are to achieve big results. For a new investor I would recommend BTC, ETH and maybe 2-3 other currencies of your choosing. Once you've wet your feet you can be a little more risky in your choices.