a) Speak as loud as you can, so people can hear you. -correct.
b)Let’s tell to her now. - In verb pattern, to tell doesn't take a preposition, so it simply uses a direct object in order to produce a complete meaning. tell é objetivo direto, nao exigindo preposição.
c) I said him I wanted to get married soon. - 'Said' doesn't allow for ths sort of construction. It usually calls for a dependent clause as compliment.e.g.: I said I wanted to leave earlier. 'said' est sendo usado nolugar de 'told' .
d) I think you need to talk him.- talk to him
e) Paula need to speak you after work. - *needs **speak to you