@ informal AMA, this was not the intention but I am happy to provide information where I can. But I need to stress that this is information and NOT legal advice. On to your questions.
1) The law actually protects unregistered trade marks (UTM). However UTMs are generally more difficult to enforce. For example registered trade marks (RTM) will give you the right throughout Nigeria to prevent a third party using an identical/similar trade mark to market a product or service that is the same as any product or service for which your RTM is registered. Whereas if you are using a UTM in Lagos and Abuja, you may find it difficult to prevent a third party using an identical/similar trademark, say in PH, unless you have evidence that people in PH also associate the UTM with your business.
So, if you can afford registration, you should do it. If you cannot, it can wait but you run the risk of a third party applying to register an identical/similar trade mark for the same product/service, and you will not be able to oppose the registration on the basis that you are using a UTM.
Investors usually check that you own all the IP to your product before they invest. Registration of your trademark may not be so important to angels, as they usually invest at idea stage, and maybe seed investors because at this stage, it is not expected that you have your house completely in order. If you have not registered the trade mark before subsequent investors come on board, it will become a point to address.
2) I presume that you meant can founders who have simply registered a business name and not a company "allot equity" among themselves. The answer is yes. The founders can sign an agreement setting out the proportions in which they will share the profits of the business. If there is no such agreement and the business is operating as a partnership, the profits will be shared equally and each founder must contribute equally to all losses. It is very risky especially from an IP perspective to operate as a partnership without an agreement. Things could get real messy and it is not recommended.
3) I have no expertise in valuing equity because accounting firms do this, not lawyers. However, I understand that in reality it is generally whatever you can negotiate with the financing co-founder is what you will get. It is likely that the financier will want the majority stake in the company, as he is taking the financial risk. You will have to accept this because unless you have a very special set of skills, finance is harder to come by. You will have to justify why you should have a higher stake. You could value sweat equity by looking at how much you would make as an employee or a service provider if you had done the work somewhere else. There are sweat equity calculators available online (like this one http://www.planprojections.com/calculators/startup-equity-calculator/) which you can use to give you an idea.