The main problems are going to be lack of 3 point hitch, lack of diff lock on the rear and tyres too small meaning as soon as you drop into the furrow, it will ground out. The earlier youtube vid is an ancient plough of some kind, which is doing a rubbish job! You need to be inverting at least 12" of soil to make ploughing worthwhile, otherwise you may as well min-till it. After ploughing you'd typically power harrow it, and for that you'd need a PTO.
For 3-4 acres I doubt its probably more cost effective to get a contractor to plough/till, but for such a small area he'd need to be doing another job in the neighbourhood to make it worth his while coming.
If its sheep farming, then yes you can get by without a tractor. Anything else and it tends to be you'd have at least 1 tractor on a smallholding. But there's so many jobs that a tractor easily does on land where you'd be looking at bodges or innovations, or just loads of hassle, with a LR. For example, baling - contractor comes, leaves the bales in the field, tractor with a bale spike on 3 point hitch can load them onto a trailer. LR can't. Spraying - easy to find a tractor mounted sprayer, you'll be fannying around for ages on the LR. Muck scraping - easy with small tractor, complete pain (lack of maneouvrability) with a LR in a shed, etc.