Hello! Let me answer a few questions you haven’t asked, while it is still not “too late”.
First, printed or engraved wedding invitations usually have two envelopes. This is so that the outer envelope can be addressed according to postal service requirements, and the inner envelope can bear the names of children, non-cohabiting lovers, and so-on that would be inappropriate to display on the outer envelope. If you aren’t going to use inner envelopes, design your invitation to have a line somewhere where you can write in this custom information — or plan to use a mail-merge so that names can be printed individually in the same font and by the same software that print the invitations.
Registry information included with the invitation, whether on the invitation itself or on an inclusion card with the invitation is not “proper”. It makes you look mercenary, as though you are out for material gain when the most important thing on your mind should be your love for your groom and your plans for a life together. Of course, having a coffeepot will make your life together much more bearable, especially on the 3120 shared Monday mornings (give or take) that lie ahead. But you need to know this: people love weddings. People love young brides. We love the idea that we can help you out and in some small way contribute positively to those 3120 Monday mornings. So we will go out of our way to find your registry (all it takes is a quick google search).
The world is also full of people — your future mother-in-law apparently not being one of them — who love throwing bridal showers. Mention in passing in the presence of a good friend or a close relative that “I kind of wish that I could have a shower, but that’s not going to be possible”, and there’s a chance that they will start finding a way to make it possible.
Your future mother-in-law is a poor representative for Texan culture, which is known for its hospitality. She ought to be inviting you down to meet the family *herself*, hosting a party (which would technically be a “reception”, not an “engagement party”, since your engagement has already been announced and then some) and offering you house-room. I would not, if I were you, rely on her etiquette advice for anything.
But you can rise above. Once you have that apartment, then you can invite members of your new Texas family over in fours and fives (or twos and threes depending on how tiny your apartment is) and get to know them over tea or brunch or dinner, any time they happen to be visiting your town.
And you can just trust, that there will be plenty of toasters and coffee-makers and fitted bedsheets among the wedding gifts that should start arriving at your apartment over the next several months — but that will probably be brought to the wedding reception instead by people who don’t know better.