need ADVICE in building something NEW in 20,000 SQ ft

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hello guys,

my family owns a 20,000 sq ft land (where 3800 is being used for two old retail stores = convenience store + lawnmower shop)...

i heard that we can use another 3200 sq ft (6000 sq ft MAXIMUM because 60% of the land needs to be used for parking) since we are NOT in downtown but are in a residential area....

we are a CPD zone...something like commercial professional...so we can build commercial, office, or retail...but we do stay right next to a residential zone with SMALL houses..and some apartments near the area....70% caucasian city with median income 70,000 income....

i have 2 questions

1) my 1st question is.....is it TOO RISKY to get rid of the two retail stores (because they're so old and ugly looking) and build a 2-story commercial 4 unit property to lease out to?

2) i would like to know and get advice in STARTING OUT BUILDING new properties...commercial....a lot of brokers have come to me and said that we should use the empty lot next to us and build something so we can lease out to renters (commercial or office or retail)...

i am very new to this so i would love to receive any kind of help from you guys even though it can just be a one-sentence advice...anything i'm willing to sponge up and learn much as possible...

thanks
BJ