Welcome, Lizbet (and fellow Corsair aficionado). I have never built a keyboard before (not sure that scratch-built stuff is my thing, but maybe, eventually, if 75% boards ever become more common), but I have modded a few now, and have tried a decent amount of switches considered to be very good. So, I would advise against Cherry MX of any kind. Kailh Box switches are smoother, and IP56 rated resistant to dust and water. The Kailh Creams switches sound nice as well, if you're going light linear, for gaming. Hopefully others will chime in as well though, since I'm a clicky guy unless I'm on my gaming rig, and I haven't bothered to do anything to my bone stock Cherry MX Red K70 for that purpose.
Is this mostly for gaming, or is there any work/productivity involved as well? I couldn't see myself using anything smaller than a 75%, even for gaming (menus), those dedicated arrow keys are too useful. You can get away with it in most things, but if you're using hotkeys in conjunction with the arrows to highlight things and/or jump around a spreadsheet ... yeah, I don't think that would be pretty. Too each their own though. I probably use arrow keys more than most people.