The list below names the locations by their vanilla bosses, but randomized bosses will appear there.
This seed is back-heavy; 5 of the 7 Star Piece are behind lategame bosses. Therefore, your strategy should be to recruit your party and then grind. The randomizer applies a 3x experience boost, so regular encounters are probably the most efficient, but only the party members you've already recruited get the XP. Don't worry about whether your party level is suitable for the final bosses, because there will be better grinds in Factory when you have all the Star Piece. Also, if you ever die, do not reset. You retain all the XP you gained.
Mario will feel really weak at his starting level and will die easily against even the earliest encounters. Go to Mushroom Kingdom and open a chest in the castle basement to find a Flower Box. Sell it for 500 coins at the Mushroom Kingdom store and buy the See Ya, which is an unlimited-use flee item. Go to Monstro Town and check the shop, which happens to have good offensive and defensive equips for Mario. Equip him and you'll be able to take on Mushroom Way and recruit your second party member, Geno.
Geno's best weapon (Star Gun) is for sale in the Nimbus Land shop, and you're going to be using Geno a lot, so it's worth the detour and price. Use some of your leftover money to shop around for some decent defensive equips for Geno. Your next party member, Bowser, is recruited after the boss in the Forest Maze. You also have to get the first Star Piece in the Kero Sewers trapped chest (Pandorite in the vanilla game). You can do whichever first.
Bowser's best weapon (Drill Claw) is for sale at the Shaman merchant in Sea. You really want to buy this. Look for chests that might have valuables inside to sell if you need more money.
You need the Bambino Bomb in the chest inside Sunken Ship (see video below) to get the 2nd Star Piece, as well as to recruit another party member, Peach. Once you acquire it, return to Moleville and make your way through the mines and beat the last boss. I don't think the minecart portion is required, so you can backtrack out after you get the Star Piece.
You can choose to recruit the last party member, Mallow. My final party was Mallow, Geno, and Bowser. Mario is definitely usable over Mallow, but his stats in this seed are so bad. I hadn't recruited Peach early enough where her XP was on par with the others, but you may find her to be a capable replacement, too. Mallow's recruitment is a single boss fight in Marrymore (sneak around the side of the chapel to get in), so it's probably worth it to have as an option.
Now that you have all the party members you want, it's time to grind. Everyone in your party gets XP even if they're not in the 3 active slots. Try them out and decide which ones you like most, and shop for good equips for them. You will also have to make a detour to pick up Castle Key #1 in Land's End. See the video below.
When you're ready, proceed to Bean Valley and defeat Megaslimax for the 3rd Star Piece. After the fight, interact with the note that the Fly Guy drops to get Castle Key #2. It will be faster and easier to backtrack out than to climb the vine to Nimbus Land.
Two of the remaining Star Pieces are in Nimbus Land, and the other two are in Bowser's Castle. Progress through both of these areas like you would in the vanilla game.
The remaining bosses in Factory are tough. A really good grind is the Ameboids. They're the blue blobs that appear. They only have 220 HP and give a decent amount of XP. You need to be able to kill them with your party before they get an attack; otherwise, they're annoying and not worth it.
If you've chosen to use Mario, his best weapon (Lazy Shell) is in Factory in one of the areas with the bolt platforms. Try falling down to discover a secret area with chests.
The second-to-last boss is Culex, this game's superboss who has been shuffled in and unfortunately gates your progression to Smithy. If you found any Rock Candies, you'll want to use them against him. It will be an annoying fight, but if you're struggling, a few extra levels from the Ameboid grind will help, or you can go shopping for strong armor. The Lazy Shell armor is out there in a chest somewhere, but I forget where. (I picked it up, so it's somewhere in my VoD.)
After Culex is Smithy. Smithy is easier than Culex, so once you beat Culex, Smithy should be no problem. GG!