Whoa, this took off to quick, and I didnt get to chime in. I wanted to start reasonably inexpensive. So there you go. You get a bag and a pot and a stove and away you go. Whats not to like? Turns out there is plenty to not like, and plenty to like as with any system. Although I will probably stick with biab, I have some considerations which I will share below for whatever thats worth. This rabbit hole is deep and I want to go in full monty but cant right now. Yes, full monty (ok not really full monty)
You move water or you move grains. Heard this once and its true. To op you are correct 20 g for 10g fv brewing. I made mistake of 15g and I can brew 10g fv but only lower gravity. For larger I have been considering topping off or sparging. Maybe even 25. I use two bags, you could use three if you like. That solves a problem right there. The easiest way to do this is a wench. Since I dont want to put a hole in my upper deck roof I use two bags. I will likely get and use a grate over the top at some point. Then you only need a kettle and the grate or huge strainer of some kind.
As it is I use a collander from the wedding pasta set over a bucket. It fits perfectly over the bucket but some wort can trickle down the sides. Then using disposable gloves I squeeze the grains into the bucket. I do this as I am heating so no time lost. So I have been considering a cooler for a while. Started a thread on this actually. Also I have no pony in this race. I am only looking for the easiest and most sensible way to get this done. Many dont understand me or this but so is life.
I mean I use a bucket and collander anyways, why not just use a cooler. Good mash temp keeping, easy cleaning, inexpensive, and so much to like. Denny conn has used the same one for like 500 batches and he seems laid back enough. This is a decent way to go. A bag in a cooler. Now is the real down and dirty. I can handily by myself lift 15 gallons of water wort around. Some of you can and some of you cant. So a pump might be required. I firmly believe smaller brewers and their ingenuity is way over looked. They provide many tips on easy brewing. I could learn a lot from them. I am more gorilla like. Honestly, I am so grateful and feel blessed to be strong enough to brew 10g easily, manually. You wouldn't know it looking at me. Looking at me you would see a chubby little 5'9 guy who thinks he is 5 10.
I digress. Combining all of these ideas and brew methods strikes me as a good way to go. I brewed 10g no chill the other day in under 2 and a half hours. With chilling I am right at 3 hours. Here is my rig. Small, tidy, fast, and effective imo. Thats it. That kettle and the element. With small bucket and collander. Your question has been answered already. A grainfather seems a clever way to go. Using a filter bag in a 3v system seems like an idea worth entertaining. Ultimately moving water or grain around without a pump or wench will be difficult. A 20g cooler and a 15g kettle would be an easy way to go fv quasi biab.