There are some clues. Like names ending in yn tend to be male whereas en are usually female e.g. Gwyn, Heddwyn, Tecwyn, Heulyn are all guys whereas Gwen, Heddwen, Seren, Elen are all girls.
Some names too that have been borrowed into the language too, so you may recognise them: Dafydd, Steffan, Deiniol (David, Stephan, Daniel) and Mari/Mair, Siân, Catrin (Mary, Jane, Catherine).
Or read up on Welsh history, get interested in Welsh current affairs or better still, get to know some Welsh people!
A good idea. This introductory course only uses one or two of these combinations, but we will work out which units have a bit of spare space in their notes to give some more examples.
Only some prepositions are combined with these 'infixed pronouns', and only a few of the combinations are covered on introductory courses. You will find more on the web or in a grammar book if you search for the topic.
You're right. There are a few common contractions of possessives in colloquial Welsh:
ei > 'i e.g. â'i chwaer "as his/her sister"
ein > 'n e.g. a'n tŷ "and our house"
eich > 'ch e.g. i'ch parti "to your party"
eu > 'u e.g. o'u gwlad "from their country"
In addition,ei "his/her" and eu "their" both become 'w after the preposition i "to/for".
i + ei > i'w dŷ "to his house"
i + ei > i'w thŷ "to her house"
i + eu > i'w tŷ "to their house"