There are books about filing a provisional patent yourself - here's an example. The provisional patent is thrown in a drawer somewhere, and a clock starts ticking; you've got a year to file, and if you do so then you get the benefit of the file date being the date of the filing of the provisional patent.

The provisional patent itself gets you zero protection. Actual protection occurs if you file the actual patent and the patent is granted. All the provisional patent gets you is that earlier filing date. You can tell investors you've filed for the provisional patent and that's worth something.

One possible issue is that when you get around to filing the actual patent, the claims of the actual patent can't exceed the claims that were made in the provisional patent. Well, you can file a separate patent with claims that do exceed them, but you don't get the benefit of the earlier filing date.

The patent would presumably be filed by the corporation, with the inventor listed as the inventor.

You can hire a patent attorney to file a provisional patent if you're not sure you want to go the full distance and pay the full cost of an actual patent application.

As to trademarks, you would want to trademark the company name and the name of the product, and if you are low on funds then you always have the choice of not registering the trademarks with the USPTO. You can just stick a "TM" next to the names and get some common law trademark protection, though there are some advantages to registering them, like a presumption the trademark is yours if the matter goes to court. Registration will cost around $650 for each mark if you do it yourself. It's good for 5 years and then you can renew it. You would want to be sure to do your own trademark search before choosing the company name and the product name. Here's the USPTO "Getting Started with Trademarks" page.

In cases of limited funds you can also do a state trademark registration, which I've never done and I don't know if it gives you any added protection beyond what a common law trademark would, if you're in Texas and somebody in Nevada starts using the mark.