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5/8 or 6/8 is a good place to start. Usually round points are recommended so you don't lose an ear, but since you've been dealing with what is effectively a spike at each end of your current set up, I'm sure you'll be ok!

You will damage your first strop. The SRD strop's are lovely. You should probably save it till you've had plenty of practise. Kenrup does a good honest starter, as does Tony Miller. Consider them too. If you want the ease of buying from one place, get the strop, but bear in mind, you will want another when you feel more proficient.