Should I try replacing the motherboard as a novice?

Only you can decide wether or not you feel comfortable proceeding. With that being said, here are a couple of points to consider:

1. Have you viewed the appropriate guide, such as this one for Repairing Liquid Damage?

2. Do you have the appropriate tools and working space? If not, can you, or will you acquire what you need?

3. For iPhones, the logic board is essentially the phone, that's why iFixit doesn't sell them. Purchasing a reliable logic board by itself can easily cost you almost as much as a new device. However, trying to properly address the potential liquid damage would cost far less.

4. I have found that eBay tends to be the "best" source for logic boards, provided that you are willing to tread carefully. If you just buy the first one that you find, you may be out of luck. If you still want to get a new logic board, make sure that you only purchase from a reputable source, and be sure that you have read and fully understand the description, condition and implications of both before proceeding with a purchase.

Good luck to you!

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