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As it is happiness based, there really isn't a good estimate for level. Just keep working on mking it happy. Keep a soothe bell on it at all times, as this increases the amount of happiness it gains. Break your bank buying vitamins, use EV lowering berries if you have them, make sure to give it a haircut every day, and keep it in the front of your party (it gains happiness every time you walk a regular number of steps) Above all, do not let it faint in battle, and do not use herbal medicines on it. There's a lady in Goldenrod city that will tell you an approximation of how happy your pokemon is. When she tells you something along the line of "The pokemon can't love you any more than it already does" you'll be close to the evolution.
That will get you to Togetic. The next step requires one of the D/P/Pt exclusive stones so be sure that you have one traded over, or you have copy of one of those game which you can use. Otherwise, the stones are very difficult to get on SS.
I would also advise you to have some heart scale at the ready.
After it learns the appropriate move that you want to keep would be the best time to evolve, yes. But, while wish is pretty good to have, Roost strikes me as being a little more reliable since there isn't a delay between use and effect. But maybe that's just me. At any rate, you should look Togepi and his evolutions up on Serebii or some similar site where you can compare the moves that the various evolutions can learn so you can plan your ideal move set out, if you haven't already.