Q: abbreviations in the abstract.
Answer:
Some journals may not allow the usage of abbreviations in the abstract. Therefore, do check your journal's author guidelines before you start writing. However, in general, it is best to avoid using abbreviations and acronyms in the abstract unless the abbreviation/acronym is commonly understood and/or is used multiple times in the abstract. If a term is used multiple times in an abstract, then of course it makes sense to introduce or define it by spelling it out the first time and use the abbreviation for subsequent repetitions.
However, not that even if you have used an abbreviation in the abstract multiple times, you have to spell it out again the first time it is used in the body of the paper.
Q: Reference in paper with space.
Answer: with space
This paper [1] introduced an IoT framework with ...