Ted, no need to worry about modern ammunition. It's convenient, but not required.
That is just the beginning. Go find the thread on custom Foxes, and look at the time, trouble, and money that have been poured into projects. A lot of guys seem to have figured out either they couldn't shoot a gun with 3" of drop, or, didn't want to.
My opinion, old guns are a lot like old cars-you have to want to use it to keep it going. Some guys get lucky, and some guys get stuck. Seen and owned good English guns that have turned into money pits, too.
All my shooting is rough shooting. I'm getting over the decoration and trying to find out what works best, and using that in the time I can dedicate to bird season, always less time than I'd like.Taking a header down an icy drainage ditch embankment is always a possibility. I figure the gun should be worth less than the medical care I need to straighten myself out after something like that.
The no-tox thing is looming large as well. I can't promise my sub gauges will survive that.
I wish you luck. When you mentioned the part about funds, something I understand all too well, the first thing that popped into my head was to tell you to find a Beretta Silver Snipe O/U in 20 gauge with 28" tubes and to never look back.
It would do the job, beautifully.
Best,
Ted