"very interested in film" and yet you are considering a device designed to capture still images and video capture is a convenience feature.
If you already know what your workaround plans are for audio and the automatic shutdown when the camera overheats, by all means, move forward - I agree learning to use the equipment to understand its limitations is extremely important. You might start by downloading and reading through the manual available for free from nikonusa.com - these issues are no secret, they are published and known items associated with nearly all low-end dSLRs.
I know several folks who went the inexpensive route you are considering - and ended up having to buy at least 3 of the same camera (one is in use while the others cool down enough to turn on). Did not save them as much as they thought. I saved and got a device designed to capture video (Sony NEX-EA50UH replaced by the NEX-EA50M) - with a large imaging sensor and interchangeable lens system (E-Mount) AND XLR audio inputs... and a handy slide-out shoulder mount... and it has a hot shoe for a flash in case I want to take stills...
And I can assure you that my HDR-AX2000 can dance circles around it as the AX2000 does a much better job under poor lighting conditions. If video is that important to you, svae your money and get a camcorder...
And we don't know what your plans are for editing - your computer may need upgrading - and your video editor is ________ and you know it can deal with the MOV files the D3300 captures... right?
You will also want to investigate lighting (you're going to need it), mics (there is no single best mic, start with a shotgun... plan on getting a wireless lavaliere - likely wireless - and a stereo mic). Throw in stedaying devices - I use a tripod, mostly, but also have a camera crane, slider and a Steadycam arm/vest system... the video capture device is only part of the larger system of stuff that all needs to work together.
Link to the manual:
http://download.nikonimglib.com/archive2/Wywwt00lh46s0109T7E089fAaV06/D3300RM_(En)02.pdf
Recording movies starts on page 155.
Page 157: overheating.
Pages 156 and 158: file size and duration limitations.
Page 157: Internal mics record camera noise, use an external mic (better yet, record the audio externally using a Zoom H5 or similar digital audio recorder and synch when editing).
Page 358: MOV Video file format
While we're here: Digital video capture has little to do with film. There is no unexposed film in canisters, no keeping the canister in a dark bag, no sending exposed film out (in a lightproof canister) for chemical processing and no digital conversion - scanning frame by frame - to computer format for editing...