C) Buying from DLsite (https://www.dlsite.com/gay
There are 2 ways to buy from there: Buying with or without an account
On the dojjin page you click on the yellow cart button and then on the cart button up above. Select the credit card button. Next page fill out the first 2 fields with your E-mail address, ignore the 3rd field and click on the button below.
You can download your file now and you'll receive an E-mail with download information should you want to re-download. This is only valid for a specific amount time and DLsite will send you a reminder when the deadline is approaching.
Click on the register option on top right of the screen. Next page enter your E-mail address and follow the steps until you're registered. Shouldn't be that complicated. Make use of your translation device for support.
The benefits for buying as a member are that you get extra credit for every purchase you do as well as when you leave review comment on the dojin you've bought. Similar to DiGiket.
And you can re-download all of your purchased dojin at any given point without a limit.
DLsite actually comes with a convenient English version (https://www.dlsite.com/ecchi-eng/
There used to be an extra English version just for gay material, but it seems to be gone now?
New dojin also take at least one week until they also appear on the English version, sometimes even not at all.
Therefore it's not that bad of an idea to register at the Japanese site. Your account is also exclusive to whichever version of the website you're using.