Money is power and for you to get that power, you need to invest,save money. You don't wake up one day and get that power, it takes a lot of financial discipline to achieve that.so I suggest you save up and buy some bitcoins for the rainy days.
Bitcoin is one thing that will not lose value rather it appreciate in value. Just invest because at old age you will not have the strength to start doing all that you were doing when young.
This means that before doing all that, you need to ensure that your finances are truly stable. If you don't have a steady income and try to invest in bitcoin, how will you support yourself? Paying for bitcoin in installments is good, but you also need to consider your livelihood. If you don't pay attention to this important matter, who will enjoy the fruits of your bitcoin investment?
Strengthening your financial foundation is far more important, and don't worry because bitcoin will always be available for you to buy.
We don't have to wait till we have a strong financial foundation before buying Bitcoin, if we are very intentional about buying Bitcoin then buying by installment with as little as we can as you said can be good while working on our financial situation simultaneously, Bitcoin will always be available but it might be higher than what it is now, we should buy Bitcoin whenever we have that spare money to buy Bitcoin
to make us become a Bitcoiner taken us off the no coiner zone and should only buy again when such money becomes available again.