It may sound a bit odd but you need to start depending on where you want to end up, ie decide whether you want to get caridina or neocaridina (or other) shrimp as they have different requirements and need different water parameters. Neocaridina are the easier shrimps and probably the best place to start. They are also cheaper to buy and set up as they don't need the buffering soil substrate, just sand or gravel etc.
You can get the tank at any time as that won't be affected by the type of shrimps, shrimps don't need depth of water so most people get shallower tanks, and there are a wide variety made specially for this purpose, though they cann be a bit more expensive. Size will depend on how much space you have but most are around 30 litres which seems to be the best all round setup for just shrimps!
The tank will need to be well run-in before getting shrimps, the normal cycle and enough time for enough biofilm to grow in the tank so even once set up you will need to run it without shrimps for very minimum of a month, preferably more though!
If you let us know what shrimps you want to get we can give you more specific advice!