Hair-growth problems
The reason horsetail (equisitem arvense) is recommended by many herbalists for healthy hair is because it is rich in silica. I prefer to combine horsetail with nettle (Urtica dioica) and oat straw (avena sativa) since these three seem to work particularly well together as a synergistic blend when it comes to getting silica and other supportive minerals and phytonutrients for hair, skin, and nails. Biotin is another wonder nutrient for hair growth, your friend is quite right. As far as it causing acne, this link has yet to be proven scientifically. However, biotin (also known as vitamin B7) is similar in structure to vitamin B5 (Pantothenic acid), and it appears that when additional B7 is introduced to the system via supplementation, it can be at the expense of the absorption of vitamin B5. Since low levels of vitamin B5 can trigger acne outbreaks in some individuals, the supplementation of biotin can indirectly lead to acne.
Fortunately, the solution is as simple as supplementing with vitamin B5 at the same time as biotin (or better, using a B-complex as you already do) and drinking more water since biotin is a water-soluble nutrient.
Getting your biotin via food sources such as egg yolks, liver, nutritional yeast, salmon, avocado, nuts, legumes, cauliflower, whole grain breads and cereals is another clever way around the acne/low B5 issue. The other typical cause of a coated tongue is candida overgrowth — the multivitamin you are taking will help to address this and restore intestinal balance.
The coating on your tongue is often a sign of dehydration, so drinking around 2-3 litres a day should help.
Red spots on the back of the tongue aren’t typically a cause for great alarm — they are often a sign that the body is fighting off the early stages of a sore throat or cold, or they may simply be the normal bumps at the back of the tongue appearing more prominently due to the coating on the rest of your tongue. I can recommend the products and methods developed by Anthony Morrocco of The Morrocco Method (www.morroccomethod.com), as these helped me immensely following the birth of my second child when I experienced the loss of a third of my hair and a cessation in hair growth. It is well worth browsing through the information on his website, especially relating to the techniques. Scalp massage and regular brushing with a natural bristled brush worked wonders for my hair!

