Good questions
1. Like bonds, do these mature at some point and the principal is paid back?
The bonds will have an indefinite maturity and can be sold / bought at any time.
You will gain interest each day for the bonds you hold, and the bonds value and interest rate can change with each day.
The daily interest rate / bond value will always be displayed for each corporation in the "Stock Market" screen.
2. If so, what is the par or face value of the bonds? Or what amount of HPD will I earn if they do mature?
You will gain the interest daily. Since the bonds have an indefinite maturity, you can hold them as much as you wish and sell them when you want.
3. Since bonds are liquid cash equivalents do they count toward your power score?
Yes, bonds value will count towards you power level at a rate of 0.8 HPD in bonds vs. 1 HPD cash. This value may change to 1 vs. 1 to reflect the risk if we put some updates later on to steal HPD from bonds market as you can now with leaking HPD from player accounts.
4. What are they weights or formula to determine the effect of the market variables on the bond price? For example if I complete a recover codes mission or cause 1,000,000 HPD in malware damage how much will they bond price change?
The effect depends greatly on the total value of the bonds that the corporation holds. For example, if the corp has a total bonds value of 300 million HPD and you do 1 mil HPD damage to one of it's servers, then there is a possibility that the bond of that corp may lower it's value by 1/300 per bond. However, each factor will also have a random part in it, making it react in uncertain ways.
5. On large buy or sell orders, what is considered large? 1,000? 1,000,000? 100,000,000?
Large is considered taking into account previous history of sales. There will also be a max increase / HPD value and a random variable. On the end of the day, the volume of sale orders / buy orders is calculated and matched with previous history records. If the volume is higher then average, bonds value may rise or stay the same, while if sales are higher then average, it could stay the same or lower a tiny bit.
Concatenating all the UP and DOWN factors will result in changes to the price / unit of bods for each corporation. News may also be issued in there, stating what was the major cause of change, like if you hit a corp with lots a malware and that was the main factor for the bond price change, a market news will say something like "Omnicron servers where hit today with heavy malware attacks. There are reports of massive economic losses. Omnicron CEO stated that an investigation was opened to find the attackers."
The news and events that happen with the bonds market could also spawn special missions, like an "Investigation" mission where you are sent to investigate an incident where a secret server was hit by malware and try to find out the servers / players responsible. And if you do find out, you'll get a nice pay and the mega-corp could use that info to place more bounty missions on the attackes...