If you are looking to finance the purchase and rehab, most hard money lenders will be able to lend to you as long as the total loan amount does not exceed 75% of the ARV and you can put 20-25% down on 1-4 units. 5+ units will require experience with several 1-4 units or 5+units 

Lenders are always competing so shop around.  

Just make sure you ask your lender and tell them in writing you're doing that - they can technically call the note due (both my lenders said it was ok to have the title changed to an LLC) but this doesn't happen often.

I'm looking for a lender who can give me a line of credit on my rental portfolio.

Looking for valuable realtors, lenders, PMs who live in the area 

Just know that your lender needs to be ok with things. 

Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

The Find a Lender tool at the top of the page is a great way to find lenders. 

But our lender is only offering us a renovation or construction loan, which I can understand.So my questions are: should we put down as much as possible to lower the monthly payment of the reno or construction loan? 

I did just that and can't find one lender who has an exposure limit loan program.