Nope it doesn't give you any issue.
Just changed the injectors.
Rest exhaust ports are same, and so are intake ports no difference in them. And throttle body of m18a is very slightly large. Like if m13 is 18mm so m18a it's around 21mm. So you can use m13a throttle for your life.
Only thing you need to replace is injectors.
Rest vvt is your choice. You've to spend 5k on computer. Baki vvt has its benefits but they're not that important, like engine can run without valve overlapping, without being damaged for like 100+k and 3-4 years.