I've never heard of Botrytis on spuds. You'll get it in the greenhouse if conditions in there are stuffy and damp and it'll attack your raspberries in wet weather, etc. It isn't a thing that rotation will limit. You just have to work with it, as you do with slugs and greenfly, etc.

As for your spuds, seed potatoes that you buy every year (and you should) are grown in cool areas such as northern Scotland where aphids are far less likely to spread virus diseases. The seed tubers are matured in the ground and are kept in cold storage over winter, treatment that has them romping away in the spring. They are tested and must be certified disease-free before they can be sold. None of this applies to your Lady Balfours. You are taking a risk, probably getting a lower yield than you should be getting and you're indulging in false economy. So good luck with that.

As for F1 seed, they are expensive to produce and are generally sold in smaller quantities per pack. They will always give you consistent results. If you want the same F1 variety (e.g., my wanting to grow Sungold tomatoes every year, an F1 variety), you must buy fresh seed. You will not get Sungold, or anything like, from seed you collect from Sungold tomatoes from your greenhouse. Most likely you will get a ragbag mixture. In addition, F1 varieties have the advantage of possessing hybrid vigour. It's all in the science and you'll just have to trust your seed company. But do have fun cutting corners, though you won't know what you'll get until it's too late to start again.