If you can't buy correctly then it will be your first mistake in Bitcoin, if your investment time is short. Your risk will increase so it is definitely best to hold for the long term to reduce the risk. Here the more longevity you invest in investing the lower the risk and the best approach for you. You will save the most if you buy bitcoins using the DCA method only, and if you collect bitcoins for the long term, your investment will be long.
We are not all aware of the exact price to buy bitcoins so we should set a fixed price and then buy accordingly and hold the investment for a long time as you have implied. Investing in Bitcoin requires us to commit to holding it for a long period of time because if we can hold this investment properly for a long period of time then we will be able to achieve the desired results. Also you mentioned risk we all have to accept that all investments involve risk. But while all investments involve risk, investing in Bitcoin is much less risky.
Investing in DCA method is easy for everyone but may not be possible for everyone as many do not have source of income due to which they cannot invest regularly. Due to which they cannot apply this method properly in the case of investment. Yes you are correct that if you invest in DCA method and hold for long time the investment will grow.
but we need to do it consistently as you said because if we don't do it correctly consistently, it will be difficult to achieve the investment targets we make and we must have good planning before deciding to invest.
You are right, it will be very difficult to be able to invest using this method if we don't have a steady income because it could be that when we have a purchasing schedule that we have set and we don't have the funds, of course we won't be able to buy according to the schedule that we have set. However, it would be better for us to buy according to our abilities and not force ourselves to buy if we are not yet able to invest.
Collecting profits by selling advisablely parts of our investment totally depends on investor level of accumulation probably at your maintenance level or have gotten to your fuck you status. Yes, at that point you can sell part of your investment and do what ever it may please you with the profit you got, Bitcoin is not a tradable coin so you don't just sell for few dollar profits on seeing the price increasing you might buy back at a price higher than your selling point, keep buying Bitcoin and hodl for as long as 4 to 10 years or more where you can have a compounded value of your investment over time before considering if you are to sell or not.