Your advice on purposely dovetailing your interests is interesting, especially contrasted with the advice I often hear about not trying to change your partner. Don't expect change, but give it?
It's a very good question and a subtle, sometimes difficult issue. IMHO:
You both are human beings. You both will be able to change in some ways and not in others; you'll be willing to change in some ways, not mind in some others, and not want to change in others (and might find you change anyway). And all change is a matter of degree; it's not binary.
You can't say in foresight what is possible, though some things are obvious. Don't expect that your free-spending, indebted partner will inevitably 'see the light' and adopt your financial discipline; but maybe they will agree to let you handle the checkbook. Your extreme introvert partner probably won't become a social host(ess), but maybe they will learn better social skills or become more comfortable and able in social situations to some degree. Or maybe the introversion will become even stronger, or come and go.
So you can't expect your partner will change in specific ways that suit you and you can't make them do it. You won't be able to change in all the ways you and they wish you could. A necessity at the start is that you happily love and accept each other as is, as real people, with warts, character flaws, and all, even when they suck and make your lives miserable - the other partner's love in those moments can change your lives.
What you can do is both have the trust and good faith to do the best you can for each other and support each other, even if it's not always 'fair' or balanced. Both change what you can and work out what you can't. Maybe you love RTS gaming and your partner doesn't, but maybe you can find interests that you both love and suit both your needs for an escape. That applies to more serious issues too, but hopefully you discuss the most important ones (e.g., kids) before making a commitment. A major step is realizing that there are things in life more important to you than you (especially more important than your pleasure), and if you do change then you'll find that many of those personal 'needs' weren't so important after all. Personally, it's a source of joy to do things for my partner, to see what I've given up and the seemingly infinite reward; it's also a source of pride, a measure of how far we've come.
EDIT: I should add, though, that IME different people have an amazingly wide variety of arrangements, explicit and implicit, in their relationships.