I would second this. Go with the biggest you can fit in your space (and afford). Upgrading from 29 to 50-ish won't feel like that much of an upgrade in space after a few months. I would recommend at least a 4 foot long tank if you have the space for it. That gives you the option to keep some medium sized fish like one of the smaller tang species. Traditional rimmed 75 gallon tanks are dirt cheap compared to rimless options, and you can get reef-ready rimmed 75 gallon tanks that are already drilled for a sump also. If you prefer the rimless style, I've heard great things about the value of Innovative Marine over Waterbox or Red Sea. Obviously almost everyone who chimes in is going to say whatever they have is great...probably some version of confirmation bias at work.I just upgraded from a 75 to a 125. I wish I had gone with a 180 or maybe even a 280. Rather than looking at a 50 I'd consider going as large as you can. I'd think about a minimum of a 65 or 75 for now. Even those are going to be small if you want any kind of fish load.
Last year I upgraded from a 46 gallon bowfront with a canister filter to an 80 gallon lagoon style (4 foot x 2 foot footprint) with a 45 gallon sump, and while the initial learning curve of plumbing a sump for the first time was steep, it definitely wasn't impossible, and I was successful on my first attempt. My maximum upgrade size was dictated by the available space in my living room, and I'm glad that I maximized that space. Feel free to take a look at my build thread for the building process and some recent tank videos if you like. Good luck!