Answer: There is no infringement of your patent, because infringement is infringement in English. It should be understood that the product produced infringes the patent right of a patent, not the patent applied for infringes the patent right. These are some conceptual misunderstandings. In addition, the improvement of existing patents, such as the improvement of basic patents, is a subordinate patent, and creative modifications and improvements can be patented (utility models are not retrieved, and if you use them in the market, there will be the problem of cross-licensing, that is, the products you produce contain all the technical characteristics of others' patents, and you infringe others' patents, but others cannot produce the patented products you apply for, so in general, both parties license each other to produce your more advanced and improved patented products, of course.
The second question, of course, others can't mention your infringement after the protection period.
For the problem of invalidation, others don't have enough evidence to show that the new technical features of your product have been made public by others, and there is no way for your improved patent to be invalid.