The strongest case for a small first deposit has nothing to do with markets. You're testing a process, signup, verification, funding, a first position and, most importantly, a withdrawal, and that test should cost as little as possible.
Run the full loop with the minimum amount. Deposit, wait, withdraw part of it and watch how long it takes to come back and whether it lands on the method you used. A platform that handles a small withdrawal cleanly is one worth scaling into gradually.
Only after that round trip does it make sense to think about size, and even then in steps rather than one move. A bigger deposit doesn't make a strategy work better, it only makes the same outcome larger in both directions.
Why the first deposit matters most
The first deposit sets the habit. An amount chosen because it's comfortable tends to lead to calmer decisions; an amount chosen because it felt like a maximum tends to lead to decisions made under pressure.
A sensible starting point
Money you wouldn't need back within a year, in an amount whose loss would sting rather than cause real damage. That's a personal figure and nobody else can set it for you.
Topping up later
Adding to a balance you already understand is a far stronger position than starting large and learning the hard way afterwards.
Questions worth asking before you send anything
How do I withdraw, and to where? What gets deducted, and by whom? Who do I contact if something looks off? A platform that answers all three clearly, in writing, is behaving as it should.
Investing carries risk, including the possible loss of some or all of the capital you put in. The value of investments can fall as well as rise, and you may get back less than you originally invested. Do not invest money you cannot afford to lose.