My baby is 4 months old and needs to move from a bassinet to a cot but we are moving out in about 2 months. Is it safe for him to sleep in a portacot for about 4~5 months till we move and settle then purchase a proper cot/bed?

Red Nose & Product Safety Australia has the following information about Portable cots.
https://rednose.org.au/article/portable-cots
https://www.productsafety.gov.au/consumers/keep-baby-safe/settle-baby-to-sleep-safely/portable-folding-cots-guide
In particular look for information about safe use &/or risks when using portable cots.
eg meeting safety standards, integrity of cot mesh & locking mechanism or any other wear & tear signs, mattress, weight of child.
Use only the mattress that comes with the portacot - do not add other mattress or soft bedding on the mattress.
Safe use of the portacot on a regular basis is dependent on checking the integrity of the portacot. A household cot is much sturdier, but understand, with the imminent move.

Is your baby rolling?
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over