DIY? Good for you!
First thing: do you live in a humid climate near the sea? If so, do NOT try to use unterminated cabling. The reason is that the salt air will oxidize the copper wire; if there is any air pollution, the problem will be worse. Your only recourse is to put solder right up the end of the insulation to protect those delicate wires and seal with shrink-wrap.
Some people use vaseline on the unterminated ends. It can work for a time, but I don't recommend it.
Second, with all the money you've saved with buying DIY cables and connectors, you've got enough left over to get decent tools. Make sure that you crimp before you solder, use the lowest temperature audio solder you can find (that's resin flux core, not acid flux core - I like WBT). and shrink-wrap the ends to retard oxidation.
To solder, put the soldering tip on one side of the connector and feed solder onto the connector where it meets the wire, ideally inside the connector itself, and then onto the wire wherever it's exposed. A good solder joint is shiny. If yours is not shiny, cut it off and try again with a new connector.
Take care to do this in a very well ventilated place, or better, outside. Keep your work at eye level to avoid the fumes. Be careful to NOT solder teflon insulated wire, because teflon decomposes into really nasty gasses. Leave that to people with special facilities. Mogami, if I remember correctly, does not use teflon.
Good luck!
