But now in 2023 the market is increasing again little by little.
Bitcoin is fighting to stay above the 17,000$, but it's still too early to call it a support level, I think...
How should I start investing right now, should I start with a small amount of money or should I start with a lot of money?
You are the best person to answer this question. Bitcoin is a risky investment, so it's advised to only invest money you can afford to lose and that you aren't going to need on the next years, neither for emergencies. If you have a lot of money under this condition, you can buy a large chunk of BTC. It's up to you. Just make sure to hold your coins in a safe spot, preferentially in a cold Ledger or Trezor wallet, what means an extra investment is needed in order to purchase it as well.