BTC is very volatile, so starting with an amount of cash and BTC, there should be a sure way to end up with more in the end.
I can see that maybe your goals are quite different than mine.
One of the best ways to assure that you have more BTC in the end is just to continue to buy it, as others have said... you buy on the dips and you DCA.
When you sell any amount of your BTC, you have to be prepared that the price is going to keep going up and those BTC will be sold forever; however, if the price happens to dip, then you can use the proceeds from the sale to buy back, but if you continue to sell on the way up, you are going to end up having fewer BTC because BTC prices are more likely to go up than down, and you do not want to be selling so much of your BTC that you end up depleting your BTC supply... so ultimately the reason for selling BTC should be for downside insurance rather than making more BTC.
I'm not spending BTC on a regular basis, however I want to buy a house soon, and if I need to dip into my BTC to do it I will.
Well yeah, there are cashflow management risks that can happen with any asset class, and surely bitcoin remains volatile as fuck, yet in my thinking any investment thesis and practice should attempt to employ as little gambling as possible, so that you are choosing when to convert an asset into dollars that is at a time of your choosing rather than just because the time has come and "fuck it"
I understand, easier said than done. Even if you have a relatively long timeline of a year or two, sometimes markets will stay irrational for too god damned long, and you don't want to be forced to cash out of bitcoin at any other time than one that you choose for yourself.
I am even guilty of a similar problem, and in early 2018, I knew that I had some relatively BIG ASS bills that would be coming due at various times in late 2018 and early 2019, so I did keep a bit larger percentage of fiat in order to cover those bills, and what ended up happening is that more of them came due all at once and they were higher amounts than I expected in November.... and fuck, what a god damned bad time to have cost overruns... so yeah, I was forced into selling a bit more BTC ... just to be sure that I was covered, including just having cash on hand in case the BTC price went lower than $3k... blah blah blah.. In the end, probably, I sold less than 3% of my BTC holdings, but still it was at a time that was not of my choosing because I had not really prepared as much as I should have for the extremes that sometimes can take place right when other shit is hitting the fan.
I'd rather avoid it, to HODL, and to not have to pay tax on it, but I feel it would be worth it.
Well, ultimately, the amount of gambling that you employ is going to be of your own choosing, and surely USD is less volatile than BTC, and surely you don't need to employ all or nothing, but you could have part in dollars and part in BTC, so that you are figuring out an adequate level of risk that you are willing to take while accounting for a variety of scenarios and really assigning realistic rather than pie in the sky probabilities to the possible scenarios.
Aside from that I've only sold BTC to pay back my initial investment, so that if it goes to 0, I'm fine with it. I've also sold a bit to buy some stuff with a BTC card, only with profits from trading.
Sometimes if all of your BTCs are in profits, anyhow, then you might feel less risk averse to just taking a chance... so yeah, let's assume for the sake of argument that your costs per BTC are $1k (for simplicity sake) and if you end up selling some BTC at $3k, then you only get 3x profits rather than 6x profits or 10x profits if things go to shit, rather than the possibility of 10x.. but still your willingness to gamble and how much you are willing to gamble can be moderated by you in such a way that is comfortable for you.. which is surely discretionary in such a way that people are going to divide that differently even when attempting to consider the matter rationally rather than just going into all or nothing gambling, which might not work out so well (but you might get lucky.. but do you want to base your finances on luck rather than really thinking through your comfort level and applying a comfortable risk so that you are mostly emotionally neutral either way?)
The thing with DCA is that I'm earning so little in cash (about median wage) that it wouldn't make a big difference,
Well, yeah, if you already have reached your BTC target accumulation level then sometimes DCA does not really seem as if it is adding a lot on the margins, but you are sounding like you are getting a bit too greedy with the way that you are talking about this whole situation. Like you want to have your cake and eat it too... which I consider to be too much gambling.
DCA remains a great long term way to continue to accumulate bitcoin, and surely if you have a decently long investment timeline, then you can invest for 5 or more years into the future... and just continue to stack away.. but if you are not really sure where you are at in terms of whether you have accumulated enough BTC or not, then you might just hodl.. and just DCA whatever the extra cash into fiat so that you have that fiat when it comes time to buy the house.. whatever that timeline happens to be.
I can do better in one good trade.
Yeah... greedy talk.
For example I had set up a buy order for 1 BTC at 4000$ just in case months ago, thinking it would never fill up, well it did.
O.k. sure.. if you get lucky, and the BTC price bounced at that spot and went up nearly 80%, then there may have been some places where you could have taken some fiat out of that, and then reset your orders back for $4k or whatever price that you believe might be possible or a long shot. It does not seem healthy to take your luck for granted and believe that you can continue to get lucky.. it is frequently better to preserve capital and to attempt to employ the capital prudently, and sure, maybe having some longshot bets in there, too... I am surely not going to talk you out of your seeming ongoing inclination towards gambling, so you just have to figure out ways to tailor your bitcoin investment in ways that suit your style and attempt to learn too in terms of ways to be as prudent as you can with your risk so that you are not ongoingly putting principle at risk.. in a kind of martingale style that really does not pay off in the long run, even if at the moment, you feel good about some of your past payoffs.
Now all that I should be giving everyone here is more merits and now virus. I'm sure I may have caught something on April the 1st from Theymos. 
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