The presence of a double-taxation agreement is an important consideration. You can use the interactive map here to find out if the country you are moving to has a DTA which covers the pillar 3a: Auswandern und Pensionskasse: So spart man Steuern - SWI swissinfo.ch
There is no limitation with regards to contributing and withdrawing in the same year. As long as you earn an OASI-elligible income, you can contribute to the pillar 3a. Withdrawals do not affect this.