Pearljen watch out for interest rate increases if you intend on refinancing. The Federal Reserve has purchased almost 3 Trillion dollars in Treasury Notes this year to drive interest rates down. This can not last and rates will return normal levels.
You can use whichever lender you want to. If you have paid for the appraisal already you will be out that money and will have to pay for another appraisal to be done. Choose the best rate, program and company to fit you!
The payment's are going to be better with the 2 seperate mortgages, but in 5 years you are going to want to refinance to put the HELOC in with the 1st mortgage and make one payment and have a fixed rate. You will then have to pay closing cost's all over again. With the 1 mortgage at the 4.99% rate the payment is not much higher and you will have a fixed rate and would not need to refinance in 5 years.