Yes, it is an adverb of indefinite frequency.
It's an adverb of time.
Only verbs have tenses (in English), and the word usually is an adverb. It has no tense.
Phrasal adverb
Yesterday is an adverb. It answers "when" something was done or happened.
historically
No, it is an adverb of time. It refers to a frequency (less than often), or not usually.
Sometimes is an adverb, an adverb of frequency.
Usually is an adverb of frequency.
No, usually is an adverb.
It can be, and usually is. In sentences such as "Let's get together sometime" it is an adverb of indefinite time. More rarely, as in "He was a longshoreman and sometime wrestler" it is an adjective.
Yes, easy can be an adverb, when it is used (colloquially) in place of the usual adverb, which is 'easily.' Example: He got off easy this time. Easy is usually an adjective. Example: I only answer the easy questions.
An adverb of place does not really have to come after an adverb of time.
Yes, tonight is an adverb. It is an adverb of time (point in time).
No, it is an adverb of indefinite time. This is another type of adverb of time.
"Usually" is not a preposition. It is an adverb that is used to indicate something that commonly or typically occurs.
In the example sentence, the word 'usually' is an adverb, modifying the verb 'is' (is how often).The word 'by' is not in the sentence, but the word 'by' functions as a preposition, introducing a prepositional phrase; for example, 'by the time he gets home' ('by the time' is a prepositional phrase).The word 'by' also functions as an adverb, for example, 'Please stand by.' (the adverb 'by' modifies the verb 'stand).
The word straight is an adverb, an adjective, and a noun.The word home is an adverb, an adjective, and a noun.The word usually is an adverb and an adjective.The word hard is an adverb and an adjective.