This should be a Highlighted Post because I preach this every day to my REI clients and my agents! As a Banker I have seen thousands of investors due days of homework and research on deals instead of letting the Banker run the numbers and most importantly the actual Approval.
Only to find out while they were running numbers, Comps, and trying to figure out rents and NOI the deal goes pending under contract and then sold! To add to what you mentioned I think more investors should first talk to a Banker and get a Pre-approval for multiple scenarios and property types.
Just because you have some money in the bank for a down payment does not mean you will be approved for the property or it will pass an appraisal. A ton of buyers realize they have good credit, have the down payment but lack reserves, landlord seasoning, or do not understand if the property is "Subject to" they will need to use a HML or do a renovation/construction loan which can change the NOI and overall deal.
Netowrking on the Bigger Pockets forum is a must and align yourself with a team of "Seasoned" professionals like a Mortgage Banker, Realtor, GC/Builder, CPA etc.