You really, really must get a good CPA to walk you through this. If you have one, fire him or her and find another one. I'm neither a lawyer or a CPA and you MUST have both for a deal like this.
The exact form of entity doesn't matter. The details vary and taxes are handled differently for different arrangements, but that affects the income produced by the company, not the money coming in.
I'm still not sure what you're trying to do. You say there's a partner involved and there are private investors involved. Please explain the role of each. I'm going to assume you and your partner going to create a company. The company will buy a property and the private investors will loan the company money for the property. But if that's not what you mean, please say what you do mean.
When someone loans you money, its not taxable. If someone invest money into your company, by buying shares in a corporation or member units in a LLC, that's not taxable either. If someone loans YOU money, that's not taxable. If someone gives you money, that's not taxable, either, though it may have consequences on their estate. So, I'm not sure why you are concerned about taxes, which is why I say you should fire your CPA if you have one.
Assuming the above arrangement, and that your investors are willing to lend you money at 6%, I'd keep that money as long as possible. You might get that rate personally if you have good credit, good income, and can get a conforming residential loan. Any other sort of loan right now is going to be at a higher rate. I'd be surprised if you can get anyone to loan you money at that rate, but certainly naive people with money do exist, and if you've found one who's willing to loan you money more power to you.
This is simple to set up. You and your partner form the LLC. In many states, that's 15 minutes and some chunk of change on the Secretary of State's web site. Then get an IRS EIN for your new LLC. Open a bank account. Put in enough cash to get the deal rolling. Make the offer. Line up the investor as a lender. Get all the paperwork to a title company. Close the deal. The LLC ends up with a deed from the seller. The LLC gives the lender (the investor) a deed of trust (or mortgage, if that's what your state does) and a promissory note. The seller gets the money. The only taxes owed are owed by the seller.
If there are multiple investors, the best approach is for them to form their own LLC. They would put their money into that LLC, and then that LLC would loan your LLC the money. That LLC is not your problem, and you're not involved in its setup.
Do spend some time on the operating agreement for your LLC. You and your partner need to work out ever little detail while you're friends so the decisions about what to do when things get rocky are in writing. Consider all the possibilities like the LLC needing more money, one of you needing money, one of you dying, getting sued and losing or getting divorced. Then, take your notes or draft operating agreement to a lawyer who deals with this sort of thing and get their input.
If you are thinking you will get investors to put money directly into your LLC, that is, buy units of the LLC, you MUST get a lawyer. If you, your partner, and these investors are all members of the company, you must have rock solid documentation and operating agreements. It would be best to do proper Regulation D securities filings. If there are just three or four of you and you all know each other intimately, then maybe you can just do a solid operating agreement with an attorney. This is NOT a DIY project. If even one of the investors is someone you just know casually, then you really MUST do those Regulation D filings. Plan on $20K or so to do those filings and all the legal work. The loan is much simpler and cheaper. This only makes sense if you're talking about raising a million bucks or more.
If you're going out to get investments from strangers, then you need to do an IPO - initial public offering. Plan on a million bucks to do that. The Reg D filing will set you up to raise money from people you know, but not strangers.
If I've misunderstood what you mean, and I probably have, straighten me out and I'll try to give better advice.
The best advice remains, though, get a good CPA and a good lawyer.