A Question about the Value of Altcoins

Hello friends. If anyone wants to skip this introductory part about me, feel free to do so!

I am pretty noob in the cryptoworld. I did my first purchase through Coinbase at 1st of December. I have tried selling them on localbitcoins thru PayPal (yeah I was dumb as a brick), so not very surprisingly I got fucked over by a scammer around 1000 $. That was a huge lesson for me where I have met with the taste and power of mighty HODLING. Recovering through my despair, I purchased more BTC from Coinbase and I sailed onwards to Binance 3 days ago. Here I really would like to thank you for the valuable input, because I have basically guided my altcoin investments from the arguments mostly presented here. My investment that was worth 650 $ several days ago now worth over 800 $! If anyone wonders my investments so far, I have around 800 ADA, 190 XRP, several IOTAs and half an ether. Additionally, I would like to purchase XTRABYTES, Stellar, Nem, Tron and possibly some EOS, QTUM and Waves.

To the question which really grinds my gears!

The question is when I monitor the coin prices in coinmarketcap, I was only looking at the USD pricing. However, I realized that to be able to withdraw your funds at the very end (I do not know for now how long I will keep my coins, but let's say some day), eventually you have to go back to USD. Granted that you can pretty much only sell BTC/ETH/LTC at this point to actually retrieve your money back which I cannot do it on binance and I have to transfer my funds to another market or sell it the big vendors like Coinbase, I felt like the USD value of your altcoin is not that important but their corresponding BTC/ETH/LTC equivalents are what matter. And yes, I know I should not be keeping my funds at an online stock, but I will change it whenever I can figure a manageable approach, however, I guess I am doomed to have several wallets to house my alts.

Can anyone who is experienced in this field shed some light on this? Does a coin's USD equivalence price hold any importance at all? Is there an optimal way -even a better way that I really haven't considered- to convert your money back to USD?

PS. I am purchasing through Coinbase, simply because I am on the waiting list of other markets and they are taking a very long time to respond! If you happen to have advice regarding a cheaper way to purchase, I lay my ears on you.

Thanks for the feedback. Much appreciated. Wish you all a happy Xmas with loads of moons!