I think 5 or 6 Shubunkins in a 300 Gallon is fine. I have about 20 in an 1100 gallon pond. The fish from a pet store are just as good as the ones from a pond supply place. How cold is your water in the winter? The fish may not like an abrupt change from the warm climate in the pet store to your current winter climate. I would wait till the water has warmed up somewhat.

Unless the WATER TEMP was comfortably in the upper 50s/60s Id wait till spring. There's a bit of stress involved in moving fish, adjusting to new place, etc. and also its good if they have a whole summer of eating bugs and fattening up for winter. Going thrutemps in 30s-40s for weeks, months on end can stress a new fish.

But more importantly than that, there is another factor that needs to be mentioned - and that is getting your nitrifying bacteria and your pond bio filtration established first - and being sure that your mechanical filtration is enough for leaves or other debris that may be falling into it - and then its best to add fish slowly, maybe 2 to start. Voice of experience here - I ignored that early last spring and had a bit of a disaster due to inadequate filtration and no nitrifying bacteria. Ammonia built up fast and it was only my stubbornness and doing almost daily 25% water changes that kept me from losing my fish (came close though).

The beneficial bacteria doesnt really get established till water temps are in 50s-60s - so all in all, I think I'd wait. Re: number, 5 or 6 Shubbies sounds perfect assuming adequate filtration/aeration - about 50 gals per fish is good.

5 shubunkins won't be 5 for long when they pop some spawn.

Make your source of fish based on which you like the look of best, assuming both sources have perky fish to look at

I personally would add a couple of Sarassa Comets to the mix they will crossbreed and your shubunks babies will have extra long fins and sometimes you get some great looking fish I had a solid blue mix breed with very long fins it was awesome. Sadly the blue heron got him and many others as well. Just killed them didn't even eat them.

Here is a link that might be useful: gabelmans gardens gallery

gardener1, I don't see any fish pics in your link, just lots of plants (pretty plants though!). I do really like the sarassa comets and will most likely get one or two of those as well. I just have to find them. The pond stores are really low on fish right now since it's not quite ponding season. I don't want to go to Petsmart, etc since their fish are kept indoors and won't be acclimated to the outside temps like the pond store fish will be.