I would say choose a method (are more than one or two) and follow it. If it is your friend's method,then so be it.
I also agree that it would help to know what plant's you have.Some places like Petco,Petsmart.offer plant's that are NOT true aquatic plant's.
Other plant's do best (See Anubia,JavaFern) if attached to wood or rock with thread ,or fishing line as opposed to being stuck too deeply into substrate.
Lot's of plant's lose leaves intially when going from submersed to totally submerged (is normal) and will sprout new growth within week's assuming condition's are favorable (light's,nutrient's)
Don't know if planted tank section is still on the menu here,but it is worth a read or perhap's Bing,google,forum that strictly addresses planted tank's.
Method I chose to follow, and that has produced good result's over a three year period was Tom Barr's NON CO2 method.
Followed it to a T and was/am pleased.
I bought dry fertilzer from Aquariumfertilizer.com (Macro/Micro package).
Walstad method is another method I have used and it too work's.Does not make any difference what type of filter is used until or unless you should decide on injecting CO2 where good circulation is important for CO2 /nutrient distribution.
For low tech,natural planted,no CO2 then fish waste ,combined with Comprehensive fertilzer like Seachem's Comprehensive,will go far in helping the plant's get the food they need .
Be aware,,a couple folk's who post here, have been banned from other forum's for giving downright wrong to dangerous advice if the health of the fishes or invert's in your tank/my tank's are primary concern.
Find somebody you trust,,and follow their advice .Research planted aquarium's.