Purchasing Betta and friends

I am going to be purchasing my betta soon and wanted to know if it is a good idea to purchase all its tank mates at the same time or just a few at a time?

Also I am looking at getting 2-3 ghost shrimp, an Otocinclus, and 3-4 neon tetra. Are these all ok with the Betta?

I also want to know if this is too many fish for a 10 gallon tank?

My last question is where to purchase my new friends. I have looked at Petco and they seem to have very healthy looking fish as well as a variety of types of bettas. I plan to look at Petsmart to see what all they have tomorrow. Petco did not have the otocinclus or the right kind of shrimp. I do not have any fish specialty stores around me and shipping is out of the question in this heat.

Thanks for any advice,
BB

the Betta ideally needs to be added last, all the fish you have listed prefer to bi in groups of 6.

ottos are very sensitive and difficult to get to eat, normally not recommended for smaller tanks as they tend to starve.

i'd get 6 neons 5 shrimps (ghost or amano) they betta may of course deside to eat the shrimp and not like the neons either, its down to the individual betta

I'd definitely rule out the Otocinclus, they need to live in a group or they just whither and die, they're so easily stressed out and need safety in numbers, plus they're very sensitive to changes in water chemistry.

The neons also need to be in a bigger group, or they'll just hide away. I agree with Lilfishie, Six is a minimum, the other problem with neons is that sometimes a betta will attack and kill them, I have had this problem in the past. Plenty of people keep them together with no problems though.