I looked into it in and Poland, Czechoslovakia, Hungary and Romania had around 500-600.000 Jews left in 1946. These could be have been used to fund the state. As these people are in general young (the Holocaust survivours was in general younger people), we would see a fast natural increase even with only near replacement level birth rate (it would give Yiddland around 2 million by 1989), and I expect the birth rate would be higher. So let's say Yiddland are set up in East Prussia, that would mean we would by 1989 see a population of 2-4 million people, which would place it on the same level as the other Baltic states. I expect a small number of Germans and Prussian Lithuanians would be allowed to stay, if they had been clearly anti-Nazi, simply because there will be a need for people who have experience in farming. In fact I would expect at first a number of Germans will be forced to stay as forced labour, and some of these will end up staying behind if they was as mentioned before clearly anti-Nazi before the war. But I expect at most these people will make up 10% of the population and likely just be Christian Yiddish speakers by modern day (they would likely call themselves Prussians). There will also be non-Jewish spouses of Jews, how the children of these couple will counted will likely be a little unclear, especially if they're Christians.
Post-1989 I expect that Yiddland will be one of the fastest growing East European countries, thanks to investment from Germany, Israel and USA. It will ikely early on see some emigration to Israel, but it will likely also see Russian Jews migrate to it, and as Israel continue having OTL trouble a number Israeli may emigrate to Yiddland. As such I expect a more stable population than the Baltic states. By 2018 it will likely have a GDP per capita of 30.000$ and be a EU member, it will be major tourist destination of American Jews. It will likely have a rather good relationship with Germany (through sometimes with a shadow over it), while I expect its relationship with Poland to be more cold. Lithuania would likely fall between these two in their relationship with Yiddland.