There are lots of arguments about this. The 45' will have everything scaled up, so sail handling is more difficult. Assistive devices, like roller furling, while a lot better than they used to be are still finicky. Ground tackle, especially, is so much larger and heavier that without mechanized assistance, you'd better be in really great shape.
Also, don't forget, all marinas rent slips by the foot. The cost difference is quite a bit between 31' and 45'.
If you go single handed, it's hard to beat something like a Pearson Triton 28'. It's really old, but it's stupidly solidly built. The sea keeping abilities of these smaller cruisers are underappreciated. Whatever one goes with, figure out how well you can heave-to in it. Lin and Larry Pardey discuss this at length in "Storm Tactics." They describe weathering shocking storms while heaving-to, and watching their sideways wake break up dangerous waves. I have no idea whether newer boats are still built to perform with this formerly common tactic.
Finicky? I wouldn't say so, maybe in the past, but they've had a lot of time to improve now. Sure, they're more likely to break or foul than a system that simply isn't there, but they are also considered by some, as with a number of other modern sailing aids, to be pretty significant safety enhancements.
Things that mean you don't have to go on deck in a heavy sea, things that save energy. It's a lot harder to get washed overboard when rolling in a headsail from the cockpit, and you're going to save a lot of energy over spending time getting up to the bow and working there.
Plus, I'd say the chance of getting whipped in the face by a stray block on a line is less in the cockpit too, and less dangerous if it happens.
John Kretchmer (https://johnkretschmersailing.com/) in one of his books said (to paraphrase, I forget his words exactly) that he thinks a working autopilot is the biggest safety enhancement you can make to your boat. It lets you save energy. Go down below, make some food or a cup of tea, keep warm. It allows you to save energy and make better decisions.
> Ground tackle, especially, is so much larger and heavier that without mechanized assistance, you'd better be in really great shape.
So… get a windlass!
