What are some things to consider when going bigger ? Do I simply multiply ingredients by 4 to get 20 gal of wort.
Pretty much
Your hop utilization will be a little different. Brew by scaling up, then adjust in the next batch.
Well, when I brew 5 gallons, I can lift everything myself. The kettle full of chilled wort, the mash tun full of wet grain and the large container full of freshly-milled grain are all lifted and moved however I need. When I brew 10-12 gallon batches, now I need a second (strong) pair of hands. If I moved bigger, I would need mechanization to move anything.
Time for a pump.
I second the pump! I’ve brewed 12.5-25g batches for a long time. When I increased my size, I just scaled it all up. I then made adjustments in my utilization. I finished a 5g BIAB setup over 2 years ago, just haven’t used it. Now I find that I brew the same styles over and over. Learning to limit O2 has really made a difference in the longevity of the beers. Some last longer than I like. I actually found that my efficiency got better, and didn’t change much depending on gravity.
boil off can be vastly different when sizing up. Alot of things you are used to lifting you cant, or shouldnt anymore. mash bed compaction can be an issue on some systems. Boil overs are a legit health concern.