Are you gonna hack in new socket/AC pipe/AC power here and there? Do those wet work first. Then lastly paint.
Painting is easy if you have the right tools and a properly sized ladder (not 5 feet nonsense) w.r.t wall height.

How good do you need the paint to be? If good paint for whole apartment circa 1k exclude materials maybe about 200 exclude ladder. Labour your ownself.

Some people just use the cheapest available paints
Aircond one if conceal pipe (copper and drain) already ready then no need hack. Otherwise same issue also.. u still gotta repaint that trench.

Wall paint two coat at 90:10 (just add a splash of water) will not be runny, if you put too much water the paint will drip everywhere.
Elcheapo is super matex - entry level RM35/7L fixed 15 colour
Standard custom colour (mix with machine) is around 90-100/5L for Nippon Easywash

Generally, 5L tong will cover two coats undiluted of a long wall (use about 4L+ for one long living room wall of 8m length x 2.4m height), balance can use on smaller wall area with doors and windows.

From experience the legs are stronger than the hands (easier to climb up) and do nicely rather than trying to hold long stick and press into the wall. Small roller easier to use (less splattering). Big roller is used for speed work but splatter more. Prep work like taping up the border area near ceiling and other stuff like door frames using the nippon skyblue colour washi tape is important to achieve nice lines and reduce oops cleanup case.

Decent developer most likely use the cheapest project price maxilite or equivalent.
Some crappy project that I went to, they use "fui sui" that is not even paint / some sort of white powder crap that when you put tape for 30 mins and wanna remove the tape, instead of tape only being removed, whole strip of the fui sui fake paint come off. No need to bother gently removing as its an impossible task.

Elcheapo paint I used:
the 35/7L fixed colour one use for cheap coverage of things like community hall refurbishment CSR project only  in apple green.
some no name light yellow to touch up 30 year old house for resale 
some cheapo gloss paint in brick red to paint over old roof edge (roof tiles) for 15 bucks/1L.. wrong purpose but kinda works "just to sell"
whole house repaint (sand down to cement to remove 30 year old paint), cheapo no name sealer, then KCC or matex white 20L tubs

As for personal long term use:
To cover over puttied surface use interior sealer to seal the putty, then only put matex over.
To cover over developer paint, just use 2 coats of the Easywash custom colour.
Easy wash can just wipe with damp cloth to remove dust. If cement dust from drilling - better vacuum the wall and use dry cloth only, otherwise grey cement will stick to the wall.
Gloss paint for walls.. ideally used for very well done surface (skim to perfection) or as a last resort in oily kitchen area or for heavy joss stick user (until ceiling all brown condition). Because the gloss really amplify all the imperfection if your wall is not perfectly flat. Hence most people use matte paint for walls.

Small roller give more even coat (in my experience) and cheaper to just throw away the refills. This one doesnt splatter much and technically if the edges taped up nicely can go 99% of the way and the few dots u can brush in or gently use the roller side also can.

Big roller you must buy the correct handle that is centered otherwise you will really have miserable time using it. Also big roller refill cost more. You'll need to spread like 2 rows of newspaper for the floor as it will splatter more.

For Nippon Paint products, if it is not very chalky then use

1 coat of 5200 Wall Sealer
2 coats of Easywash or other finishing as per your preference

If it is very chalky/powdery, I would advise using solvent base sealer such as Hi-bond wall sealer or 5170 acrylic wall sealer to replace 5200 wall sealer. However you have to ensure good air flow for your house and nobody staying in it for some times as solvent based paint can be really smelly.