Vanguard has funds that have early redemption fees of up to 1%. I think some of the Fidelity funds charge up to 2%. One can avoid these fees by holding your shares the required minimum amount of time.
You didn't state which funds you are working with because if you did, we could probably be more helpful. For example, if you bought a Vanguard fund at Fidelity, then there would be the commission which is an expense. If you bought a Fidelity fund at Vanguard there would be the commission as well. However, if you buy a Vanguard fund at Vanguard, there is no commission.
If you buy a stock or fund that trades like a stock, then you may have the commission, the bid-ask spread and the discount/premium to net asset value to take into account.
If this is a taxable account, you should know that many of the Vanguard funds are about to pay dividends. If you "buy the dividend" you will incur a tax cost. You want to make sure that your stock dividends are "qualified" which means you need to hold the underlying security for 60 days in the 121 day window of time centered on the dividend payout (or maybe date of record).
I imagine most of these things you don't have to worry about except when you need to worry about them.