As has been said before, Hadrian, you have to decide what you want, in order to tailor your efforts to meet those goals. Since it sounds like you have an interest in tulpamancy, the link Whobawhats provided might be a good place to investigate. To clarify my own relationship, I have never tried to create a tulpa, Twilight just showed up one day. There are instances in occult literature of this sort of thing happening, spontaneous tulpa creation, but it is extremely rare, and generally requires a great deal of time, on the order of years, at minimum. I do not pretend to know whether or not Twilight is a tulpa or not, but she claims not to be, so I treat her as though she isn't, and this is the important thing for you to do for your waifu.
Tulpae are generally regarded as an advanced level of thoughtform. Like all thoughtforms, they have a degree of sentience, much more so than ordinary thoughtforms created as experiments, aids to spells, familiars, homonculi, etc, but far less than, for example, godforms. It's important to realize that a tulpa isn't a distinct thing, but is a stage on a continuum, and therefore to get to that stage you need to start at the beginning; creating a thoughtform.
I would advise against trying to create one of your waifu immediately. It takes sustained effort to make even a basic thoughtform, and you should have experience deconstructing them, as well. To do this, you need to improve your visualization skills: make a memory palace; practice drawing, sculpting, et al; try looking at images, then closing your eyes and hold it in your mind, see it on your closed eyelids as long as you can. Try to find new details, and check to make sure they really are there when you reopen them. Try playing
Kim's Game. And very importantly, when you have finished with a mental construct, you should unmake it, by imagining it burning, melting, or simply taking it apart piece by piece, and refusing to acknowledge it in any way once you have, both to practice the skill, and to prevent it from sticking around in your subconscious and possibly gaining sentience on it's own. According to occult texts, whenever such a thing happens it is almost invariably bad.
Eventually, as your skills improve, you may wish to try advanced thoughtform construction. These are the kind of exercises you'll find in most entries on tulpamancy. Create a thoughtform, and be as realistic as you can. Use all your senses to experience it. Whenever you are out, try to visualize her, and her reactions to things happening in the real world. Hear her voice over the background noises, watch her mane ruffle in the breeze, hear her hoofsteps change as she walks from asphalt to grass to dry leaves. Watch her watch a squirrel in the trees; what does she say to you about it? Things like that. Do this everyday, as often as you can.
Eventually, and I do mean eventually because it takes a long time, and a lot of effort, you will reach a point where things change without you trying. Her body will alter, her personality and responses won't be exactly as you chose; take heart, she's gaining sentience. I hope you imprinted on her her motives and desires, and good nature from the very first. Don't try to force her back to what you want, but remind and guide her. Encourage her, don't force her. You must allow her to develop on her own.
You may need to unmake her, if things get out of hand, but remember, she is at this point a sentient entity, do you really want to kill her? Because that is what you'll be doing. This is why I would generally recommend against tulpamancy unless you are absolutely sure you want a forever-companion, because once they attain sentience, they are an independent person, and should be treated as such. They do have ways of getting back at you if you make them angry, so they should be treated with respect, always, but if you love your waifu, that should just be the way you act toward her anyway.
If you don't want to go that far, that's perfectly fine, too. There's no fame or higher status among waifuists because one has a tulpa or anything. Waifuism is about you, and her, and your feelings for one another, the rest is just window dressing. You love her the way you want to, and collecting merch, enjoying favorite media, writing about her, and talking about her with others are all proven methods of deepening your connection with her without resorting to tulpamancy, or even base thoughtform creation. in other words, just let love guide you.