Q. Is there an issue on painting or renovating one’s home during Sefira days or acquiring then a new car or expensive clothing that one recites the blessing of ‘Shehecheyanu’ on them?

A. Mishna Berura (493: 2) rules that it is permissible to recite the brocho of Shehechiyanu during sefira.
Altough in principle one can recite Shehechyanu during the Sefira days, as it does not maintain the Avelus stringencies of the Three Weeks of Tamuz and Av. Yet some Poskim do mention avoiding great moments of joy as weddings are. (See Piskei Teshuvos 493: 2)

HoRav Ovadya Yosef zt’l (Yechaveh Da’at I:24) also opines that significant and momentous occasions, should be avoided. See also Nitei Gavriel (55: 7: 8).
Horav Shlomo Miller’s Shlit’a opinion is similar.

Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a