Is it permissible for the lender to receive financial compensation for the psychological and material damages incurred due to the debtor's delay in repaying the due amount, and is it permissible for him to deduct additional expenses from the amount recovered after the debt is paid through legal means?

You are not permitted to pressure a debtor who is in hardship or to take him to court, due to the Almighty’s saying: "And if there is one in hardship, then [let there be] postponement until [a time of] ease." As for a wealthy debtor who procrastinates, it is permissible to take him to court. It is also permissible for you to take compensation for what you spent in litigation, but you must refer the matter to the judiciary to determine the extent of the damage. As for counting what you spent on purchasing the equipment against your partner, it depends: If what you spent was obligatory for you by virtue of the partnership or as a donation, then you cannot claim it back from him. However, if you spent something that was not obligatory for you under the partnership agreement, intending to claim it back from your partner, then you may count it against him.