What are some potential implications to get Studio Condo / 1BR as the first matrimonial house?

Which studio/1BR condos are you looking at? It's surprising to hear that there's a condo cheaper than resale HDBs.

Also bear in mind that with the Enhanced CPF Housing Grant, you can now get more in subsidies for resale flats in mature estates. Factoring that in, would resale HDBs still be too expensive?

As Elijah mentioned, you can't apply for a BTO within 30 months of selling off your condo. That applies to HDB grant applications, too.

Another alternative would be to consider Sale of Balance or Re-offer of Balance Flats. The wait times are shorter than those of BTOs.

If you have owned or disposed of a non-HDB property within the past 30 months, you won't be able to apply for a new BTO. Do take a look here:

https://www.hdb.gov.sg/cs/infoweb/residential/b...
This implies that after disposing of your condo, you will need to rent for 2.5 years before being eligible to apply for a new BTO.

Also, as time passes, your combined salary will likely increase and might be beyond the BTO income ceiling, disqualifying you from getting a BTO.

However, barring these conditions, if you meet all eligibility criteria, you will ballot for a BTO just like any other first-timer.