Dividing a batch into 5 different hop flavors.

1) Use Magnum or something like Columbus, or even Co2 hop extract to bitter.
2) Depends on what you want to do. If you want single hop for flavor and aroma, then you are looking at 5 different boiling pots and batches. Otherwise, if just dry hopping, one batch, split, ferment and dry hop each jug.
3) See Point 2.
4) Use a program or some math and figure what you want for IBU's. You'd have to adjust accordingly for late hop additions if going that route, to keep the IBU's the same. Otherwise, use weight, and you'll be able to tell how some hops are more powerful in flavor and bittering than others. Your choice.
5) Not sure what you are asking.. Extract batch? You mention doing mini mashes, and I"m assuming you do full boils?
6) British Bitters recipe sounds odd to want to use a bunch of american hops to try out. I"d do a simple pale, or blonde recipe.
7} What haven't you tried? American only? English? Aussie? German? I'd do Amarillo, Simcoe, Mosaic and Chinook and Centennial for American. Mandarina Bavaria and Herkules and some of the new German stuff sounds nice. Kohatu, Galaxy, Nelson Sauvin, Wakatu, are all Aussie/NZ hops that are fantastic. Skys the limit, research commercial beers, or even hop varieties and see what you think sounds good.

 

In addition to the expert advice given by @FATC1TY , I offer these tidbits.

The easiest and quickest way to sample hops is to try some Dry Hopped Bud Light. My brew club did this with good results, plus you can mix and match. Want to try Amarillo with Saaz? . . . no problem. This is the DH effect of hops but I find the flavor effects (late additions) follow the same pattern. Keep good notes and you have a master list of hop aromas. If your pysche just won't let BL past your lips then substitute Amstel Light which is equally bland. (I never swallowed, just spat out the BL)

Practically speaking, dividing a 5 gallon batch late in the boil into 5 separate batches is a daunting task. Unless you have lots of equipment and helpers this will overwhelm a single brewer. You are now worried about timing, whirlpooling, chilling, multiplied by five. I've split off a single one gallon batch (late) and that was a handful. Remember, if the brew process suffers the test becomes iffy at best.

I have fermented multiple one gallon batches (testing yeasts) and yes, you DH by just throwing the hops in the jug. But don't get hung up on IBUs. For DH'ing the alpha acid does not matter, it's the oils you are interested in. So something like Cascade is more powerful than Magnum in this phase.

The big problem with one gallon jugs is the difficulty in racking. You're only going to fill to about 0.75 gallon to leave a decent headspace. You will have trub and lots of hop debris to rack from, plus your conventional auto-siphon is not made to go into the narrow neckspace of a 1 gallon'er (try it). I've used the thinner ss racking cane but it's still tricky . . . expect to get a max of 6 bottles per jug.

If determined to have multiple fermentors I would use 3 gallon BB. That would give you a decent amount (2.XX gallon), and easy to rack. IMO, once you master hop aroma you will want to move on to testing yeast strains.

 

I suggest that the simplest approach to this experiment might be to simply brew 5 separate all-extract batches (using light or possibly amber dme). Just measure out water, dme, and hops separately for each batch. A 20 minute boil would be sufficient to get some bittering and some flavor from a 20 minute addition, and then you could do 10 and 0 minute additions (or whatever strikes your fancy for the late additions). Each batch would probably take about 1 hour, with less overall time/batch possible if parallel processing) Take a packet of US-05 and split it 5 ways.

 

Sounds like you haven't really given it much thought on what you want to get from the different hops.

I'd suggest this then:

Brew your extract beer, with steeping grains. Normal 5 gallon batch. Use Columbus to bitter, add some simple cascade at 15 or 10 minutes, and then chill the beer down. A simple pale ale, or blonde recipe kit will be plenty good enough. Bitter it to around 30-35 IBU's.

Pitch the yeast, and then split each gallon into your jugs.

Dryhop the beers with an ounce of your selected hops once fermentation is winding down. Do it in the jugs. After a week, put them in the fridge and crash it down, to get most of the hop debris to drop clear.

That will give you a pretty bland, but somewhat generic beer base that can be highlighted by the aroma, and flavor of the dry hops.


Minimal work, other than pouring your wort into the jugs, and dry hopping 5 different jugs.