Would conversion from RCC to CoE be a big shock?
Not hugely. Remember though that in any one town, there may be several Anglican churches and they can all feel different. One might seem closer to RCC (and consider itself part of the Catholic 'family', one of the three main branches together with Orthodox), one might seem very protestant, even clapping, handwaving and dancing and another somewhere in the middle. In their spiritual ethos, 'Broad Church' (in the middle) and 'High Church' have a lot of common ground between the RCC, the Orthodox and even the Lutherans.
People often say that the RCC asks a lot and expects little, whereas the Anglicans ask little but expect a lot. Remember also that the RCC has a lot of differences in tone from country to country - the concept of the 'local church', promoted at the second Vatican council by (then) Bishop Wojtyła. The RCC in Britain can have a very Irish feel - many of the worshippers and the clergy have strong links there.
There is an Anglican presence in Poland. Before the war it was bigger (1800 families in Warsaw and even more in Białystok). In Białystok it was particularly popular among families who'd converted from Judaism but didn't want the hostility from some nationalistic RCC laypeople and clergy. Now there are parishes in Warsaw and Gdansk - fairly small ones, with a mix of foreigners and Poles attending.
A close friend who is a CofE priest in England has a small number of people from Poland who arrived in the post-2004 migration who have found their spiritual home in his church. Normally when RCs come he tries to steer them back towards the RCC however some choose to stay. His church, by the way, is Catholic in ethos and packed full of people on a Sunday.
You'll find that laypeople play a greater role in the organised life of the church - it's run democratically and there tends to be more discussion, negotiation and civilised disagreement with the parish priest than you may be used to - much depends on the 'tone' of the church (see the first paragraph). Worth attending several parishes to find what you like. I tend to prefer the traditional. You'll also find (except in the 'happy clappy' evangelical parishes) a greater acceptance of LGBT people and no stigma about living outside wedlock etc. Most Anglican churches (especially the 'high church' AngloCatholic ones) are very reflective and quietly spiritual in their worship.
You don't actually need to convert formally - Roman Catholics are allowed by the CofE to receive the sacraments in Anglican Churches. If you want to convert in Poland though, you'll need to go to a country with a larger Anglican presence if you want to be officially received in the church - this is a rule that the Diocese of Gibraltar in Europe (covers Poland) have. You will also need Confirmation (Bierzmowania) if you want to regularly receive the sacrament at an Anglican Mass - not a hard and fast requirement but certainly expected. Confirmation received in an RCC church is acceptable. 'Happy Clappy' churches may well be different.
To get a feel of it all, read Joanna Trollop, AN Wilson's
Unguarded Hours (a very funny novel) or even better Susan Howatch's
Starbridge novels - deeply spiritual as well as a very good read. Also, for a Polish comparison, think about the Mariawici Church, a religious denomination with some similarities to Anglo-Catholicism.
