I am fairly new as well but I agree with @Anthony Hurlburt. Step one is to run the numbers.
1) what would property be worth post rehab
2) how much would the rehab cost
3) what would the units rent for
4) what would be you ongoing costs
5) will the cash flow cover the cost of financing the down payment and rehab costs
If the numbers make sense, then you figure out how to finance the deal.
Scenario:
Let's assume you need to go to a bank to get financing on the property and you need to access equity from your primary residence for the down payment and rehab costs.
$300k purchase price with 80% LTV mortgage
$65k for down payment and closing costs
$35k rehab budget
All in you need $100k in order to close and get the house rent ready based on the rehab budget. You decide to be conservative and pull $125k out of your primary residence in case the rehab goes over budget. When it is all said and done, you go a little over budget and the rehab costs $45k so you end up actually needing $110k in total.
HELOC vs Mortgage on primary residence:
Personally, in your situation I would get a HELOC instead of a mortgage against your primary residence. Although the rate on the HELOC may be slightly higher than on the mortgage, The reason I would use a HELOC is that with a mortgage you have a locked in payment and are paying interest on the amount of the mortgage no matter whether you use all of the money or not but with a HELOC you are only paying interest for the amount of the money you are using.
If you pulled the money out of your house using a mortgage, you would be locked in to a payment for the term of the loan on the entire $125k even though you only needed $110k. Also, the mortgage would be accruing interest and you would be responsible for the payment from the time you close on the mortgage.
Now if you use a HELOC instead, you would have only pulled out $110k of the $125k HELOC. You would only be responsible for interest and payments based on the $110k instead of the entire $125k. Also, the HELOC would not start accruing interest until you actually pulled the money out along the way throughout the project.