Hi and welcome
Yeah Puerto Ricans and virtually all other Cubensis varieties behave similarly enough to ignore the whole variety thing as a curiosity. Sure, colonization rates or other tendencies like making few big mushrooms or very many small ones can vary (between varieties but also in general!)... but actually the total weight of the mushrooms tends to be overall the same under the same growing circumstances. So don't let any of that distract you. Cube varieties (people call them strains, such as Puerto Rican) are often based on where they are found in the world. Again: you don't need someone with experience with Puerto Ricans, treat them the same as other Cubensis varieties. Not sure if or where you read/heard that you need to give them special treatment.
PF Tek is fine. If you have invested in shoulderless jars and all that, it can be simple to just use all that gear again and stick to the tek. If you are just feeling like trying different methods, for fun, getting experience etc... you can do that too.
BRF is a good nutrient source because the 'brown' part means that you get the full grain. You could use other types of grains [their flours] as well, but they should be 'brown' too, meaning
whole grain. The grain kernel itself provides mostly the energy, in bran and germ part contain more proteins and also other minor nutrients.
I can't really recommend manure for several reasons and think it is a bit advanced though I think it can be among the most effective substrates for cubes. Hay doesn't appeal to me.
Personally I advanced to other whole grains after PF in the form of birdseed (usually referred to as WBS but I'm not sure what the seeds I have used are actually for... chickens I think). You shouldn't use just any random seedmix because some seeds and grains are much more desirable than others and it needs to be free of fungicides... but I like it very much: you can shake the grains to mix them for faster colonization... doesn't contain inert material like verm... doesn't make a cake you have to be able to get out of the container it's in.. so you can just use filterbags and put in a little or a lot. I use my shoulderless jars for smaller batches or spawn, too.
I have used those seeds for Cubensis in the past but now primarily grow gourmet mushroom species (I still use the seeds to make spawn for that though I have to fruit them on wood-based substrates which is not for Cubes).
Basically the process is this: you soak the seeds overnight (or longer) in a bucket of water, it can even ferment a little just don't let it get moldy or something. Discard floating seeds by the way. Wash the seeds well until they don't make the water murky anymore. You can do this before the soak if the soak makes the seeds a bit mushy. You want to wash out the dirt and debris, not seed matter.
Pour off all the water, put the seeds in filter bags and/or jars and leave plenty of room in the 'neck' where the filter is etc. Put in a piece of tyvek (like what the outside of bubble envelopes are made of: the hard to tear plastic kind, not paper based) in the upper part and fold the 'neck' of the bag zigzag, tie it down with a piece of rope. Sterilize in a pressure cooker for iirc up to 90 minutes?
Inoculate in a glovebox / still air box. You can clone (also on agar) or use spores from a syringe which you can make from a sporeprint (also in glovebox). You let it colonize to get spawn. Then basically you use that spawn to inoculate an even larger amount of seeds sterilized the same way. You can add things like gypsum, maybe bran or other things depending.
You can use it similar to crumbled cakes, and case it.
Watch some of RR's videos called "Let's grow mushrooms!". If you are smart you can find it with good availability.
Also use the Shroomery website, it's just very good for all things mushroom. Maybe do some research first so that you get a good understanding of other techniques before you try them or buy supplies for them.
